You have my attention! I agree with everything Aurkus said, come to that. However, I do have to say that zombie butt sounds extra dirty and extra smelly. On the other hand, if it's a well-preserved and cleaned zombie, I bet rigour mortis would have those glorious green glutes extra firm!
Some people can make it look good, but there are others who I think were better off not having drawn it at all.
I think it's in your style and repertoire of "monsters" to give it a try; it's all up to you.