I have yet to inspect my own hamster close enough to ascertain whether or not they have a belly button. However, a trip around the internet has proven fruitful. They do have very small belly buttons, and they get covered up by little hamster fat rolls and fur. I would post links but I cannot. If your interest in the “navel area” of hamsters compels you further please check out ‘The Hamster Handbook’ by Patricia Pope Bartlett.