Do healing spells damage undead and vice versa?

Not that I know of. hell, I've been known to cast healing spells on my summoned undead, rather than summon new ones, particularly when the particular hurt undead monster in question is particularly useful. That is, he's largely immune to the sort of damage that most of the enemies are inflicting, I'd rather keep this undead monster alive than risk summoning a new one that might actually be vulnerable to the damage being inflcted by the current enemies.