Of couse zombies poop. Why is this even a question? You take stuff in, other stuff comes out. On BtVS, Spike would have had to poop out all of those blooming onions. Angel, on the other hand, would not have needed to poop. He never ate. I'm sure the same rule is good for zombies - both zombies and vamps are, you know, living dead.

And I'm hanging my head in shame. Check your email. :(