The whole monsters fighting other monsters is supposed to happen, i'm sure that in some interview or another somone mentioned that there would be interspecies battles. Think about really life, there are few wild animals that can live with each other.

I'm unsure about the Giza bunnies cure thing. Its possible that its a mistaken gambit, but remember that there have been other enemies in the FF series that cure you. I think the Giza bunnies are just another example of that.