Yes, in the wild they will eat snakes, lizards, birds, etc. In captivity a little white chicken meat (no bones) is a good source of protein as is mealworms.
Some monkeys do eat (or primates better said) chimpanzees are even caught on film ripping limbs from their own kind, and will lead to death. They'll eat the carcass and so that answers ur q.
A surge in monkey meat popularity has gripped residents of the Ruvuma region which marks Tanzania's southern border with Mozambique. It seems residents here are choosing to eat monkey meat instead of...