They dont do anything... except the crocodiles somehow trap you in their mouth. i dont get it, but i just relog. otherwise, i cant kill them, push them, hurt them, they are just there. idk, but i think its fine
Mo' Creatures only shows up on their screen. If they do gain an item from it, it disappears immediately afterwards. Similarly, you can put the crafting recipe for a mod's item, and it will appear for a split-second.