I ll try benign and at peace with wildlife, but wow, I have no idea if DF allows me to play an undead race at all.
Next test would be to have a single, not-opposed-to-life dude you need to keep alive (like the dungeon heart in Dungeon Keeper), wall him in, and then turn all the rest of your fort opposed to life. They would attack him, and if he dies, you lose, so you need to keep him in his own, secluded room. But maybe thats a solution. ^^
CRAZED: Crazed people even attack other crazed ones... and wouldnt be allied with undeads. The point is to make evil biomes, tombs, necromancer towers and so on friendly to them.
EDIT: I GOT IT. Just raided a tomb, no one cared. Embarked on a tower, has 10 friendly necromancers and 130 undead running around (killing the two aurochs that pulled the wagon). I then walked into the tower, no problem. I killed an osprey (wildlife), reanimated it, no problem. Warlocks not even afraid of anything. They dont care.
The opposed to life civ-members (skeletons) wont do labors, which is another thing to look at. But all in all I am quite happy with the result. Tombs, Towers and evil biomes are certainly allied with you.
Another funny thing: The opposed to life civ-members ignore my pets, but the normal undead attack them. Maybe I need special pets, which are undeadish as well for this race.
Havent tested turning pets into not_living or opposed_to_life things yet.