I will be mimicking Maynards color system to rank synergy with our Venator Reivers, though I have eliminated the "Red" tier for the unit. For those of you who are unfamiliar:
Brown - Little to no synergy with the model(s) in question. They may have potential, but not without outside assistance (IE another model buffing them/debuffing enemies).
Green - Decent synergy. Has the potential to be good given certain circumstances.
Blue - Superior match. These models have abilities and stats that directly complement each other or were made to be played with each other.
Red will indicate a new segment.
With that out of the way I will begin.
Venator Reivers are the go-to Skorne ranged unit. In a culture that values honor over anything else, the Reivers have found themselves pretty low on the Skorne food chain. They have, however, begun to earn respect among their comrades as the importance of ranged combat has become increasingly more important in the Skorne campaign in the west.
The Reivers, as mentioned, are a staple ranged unit. They do not have many fancy tricks by themselves, but if used properly they are more than capable of making their presence be felt on the battlefield.
The Reivers are lightly armored, allowing them to be a fairly mobile firing force with their average speed. They sport low STR and MAT stats, but both of those are irrelevant to our firing squad. Their RAT is a bit on the low end at 5, but they are capable of mitigating that without an outside source. They have fairly average defense and have sub-par armor, falling to AOEs fairly easily if left unprotected. Their command is average (below-par for Skorne) at a score of 8 and they are a bit pricey for basic infantry at 5/9 points for 6/10 infantrymen.
Weapons and Equipment
Reivers come armed (as their name might imply to those skilled in detection) with reivers. A reiver is essentially Skorne's answer to western rifles. The Venator's guns have decent range at 12'' which gives them a threat range of 18''. Their POW is a bit low at a score of 10, but the gun receives +1 to its damage rolls against medium based models and +2 to its damage rolls against large base models. Not game breaking, but nifty. The weapons are ROF1 and each Reiver comes equipped with one gun.
Reivers are also equipped with a basic sword, but at MAT5 and POW8 it should only be used in dire circumstances.
Venator Reivers themselves only have one innate ability and it is the only thing that keeps them from being a below-average unit: Combined Ranged Attack. This, as most of us know, allows multiple Venators to combine their fire on a single target. Mixed with Burst Fire (the bonus damage vs larger bases) this allows the unit to build up damage quickly; six of them hitting a large based model for a POW18 attack. This also makes them passable against non-stealthed infantrymen, though you will have to at least combine in pairs to get results and are then (depending on the situation) using resources poorly.
The following is a overall rating of how much synergy the Venator Reivers have with other Skorne units. To those of you who may not know synergy is just a way of saying how well one component works with another.
Cataphract Arcuarii - The Arcuarii are, themselves, a ranged unit and are likely to be flanking your opponent. I would not recommend using them to babysit your Reivers.
Cataphract Cetratii - A solid wall to put between you and the enemy. The only problem is you cannot shoot through their medium bases (unless firing at a large base). There are ways to allow your units to draw line of sight through each other, so this problem is not insurmountable.
Immortals - Not a lot going on here. Immortals excel at receiving charges then countering in return. You may use them to defend your Reivers but I would never do so if a better option was available.
[COLOR="Sienna"Blo]Paingiver odrunners -[/COLOR] I'm sure your stealthy DEF14/ARM11 ninja assassins will do a marvelous job supporting your gunline. Smells like sarcasm.
Paingiver Beast Handlers - Two units made to do perform completely different tasks. The Paingivers may not mind having an extra line of bodies in front of them though.
Praetorian Ferox - This unit is designed to operate on its own. Their high speed will quickly leave the Venators in the dust. The Venators may soften a target up for them first, but it is nothing a different unit wouldn't be able to do.
Praetorian Karax - Plenty of bodies to protect your flimsy gunmen, decent enough armor to potentially stay there, girded to save said flimsy gunmen from blast damage, these guys are where its at for supporting Reivers. They need no external buffs to form their ranks and block charges/LOS to your Reivers.
Praetorian Swordsmen - With their unit attachment your Reivers may shoot through your Swordsmen. If you plan to employ this tactic you are, however, spending more points on a unit that will be less effective at guarding your ranged units.
Tyrant Commander & Standard Bearer - Excellent unit to have in tow of your Venators. Their normal-move-speed buff will allow your Reivers an even greater threat range (20'') as well as giving them pathfinder if needed. They can also cause units to stand up, but that ability is not likely to see a lot of use on our non-tough Reivers.
Venator Catapult Crew - While they do both reside in the same caste; the Catapult and the Reivers do not have much to go on aside from them both being ranged units. The Venator Catapult Crew can, however, take advantage of many of the same synergies that the Reivers themselves enjoy. IE: It only takes one unit of Karax to block your Catapult and your Reivers.
There is no one solo that terribly stands out when thinking of the Reivers. There are some solos who can take advantage of the Reivers, though the relationship may not be mutual (it may be parasitic even).
Agonizer - I hesitated to even consider this green. The debuffs to warbeasts will most likely not be able to save your Reivers should that Warpwolf manage to get its hands on them. The focus negation, however, can stop your Reivers from getting toppled like a house of cards by a warjack. Without focus to boost most warjacks will also only hit 50% of the time, give or take.
Ancestral Guardian - This is the aforementioned parasite. He can do a decent job at protecting the Reivers, but you probably won't want him way in the back. The Reivers will provide souls for him to munch on if you "fail" to protect them.
Extoller Soulward - Like the Ancestral Guardian the Extoller Soulward has a parasitic relationship with the Venator Reivers in that it can receive souls from them when/if they perish. As pointed out by Indragnir, the granted Eyeless Sight and Magical Weapon properties will only affect one model, and only one model will benefit from the effects if you decide to make combined ranged attacks. The ability is better used on other models, specifically a single ranged model such as the Titan Canonneer, Basilisk Drake, or any single model that needs LOS to charge into a forest.
Paingiver Bloodrunner Master Tormentor - Not a lot to do here. They both kill things, but neither model(s) can do anything to directly support the other. The Master Tormentor will actually engage units giving them +4DEF against your Reivers. Not a great combo.
Void Spirit - See "Master Tormentor".
Tyrant Rhadeim This was orange initially, but with his Commander ability to keep your Reivers in check, and a heavy hitting attack to finish off a big target (something the Reivers are good at damaging) I placed him in the midfield for synergy. He is a bit pricey so I would consider other options before Rhadeim himself.