My friend knew a german shepherd dog who was given raw hide bones, and the dog ate an entire one. Then he stopped eating and got really sick, so the owner took him to the vet and the vet told him that the bone had gone into his stomach, and the rawhide had soaked up all the juices in his stomach, causing it to swell. So it was stuck in his intestines and he needed to have surgery to get it out If you ever put one in water, you will see it get bigger.

Other than scary incedents like that, I don't think rawhide is a bad thing, just maybe some types or shapes or something.