Its something of a corner case, but I had it come up in a practice game yesterday.
Siege had popped his feat, and a grenadier decided to start dropping AOEs onto my stealthed mage hunters, some of which were standing within Discordia's bubble and one of the AOEs drifted onto Discordia.
Now obviously Discordia didn't suffer any damage from said attack, however the question that came up was if he still suffered a damage roll (and thus burned off the one time half armour effect of Siege's feat).
Discordia's effect says (and this is the same for models with Dig In and for Battle Mages) that this model does not suffer blast damage. It does not say that a damage roll is not made, just that the model does not suffer the damage.
When an AOE with automatic fire (such as from a Vanquisher) lands on them they still suffer the Fire continuous effect which is an effect of the AOE, my question is if Breach is considered to be an effect of the attack.