There were some druid feats in a dragon magazine that went along with some of the vile stuff from book of vile darkness - one of them was the ability to sacrifice animals to cast divinations.. I don't feel up to looking it up myself, but maybe it will spark someone else's memory and they will tell you where to look.
blighter is also the only undead-related druid prestige class I can think of, but you lose most of your original druidic abilities doing it, and all your undead abilities relate to undead animals, I believe.
/ali