With regards to bless, I suspect they have something sorted as that would be an obvious thing coming up in a play test. It should be noted they have already stated that not all healing damages the undead. They can heal from both poison and necromancy. I would expect blessed surfaces to simply have no effect at all on the undead (from a balance perspective it would be terrible it if damaged and from a lore perspective it would be inconsistent if it still healed).
But hey, if Larian hasn't thought about this yet then I expect a quick patch as everyone playing the undead dies instantly when they get to the first automatic appearance of the blessed surfaces :p
The undead don't have the "zombie" talent in that all healing damages them, it is just "good" healing that does.
