You ask, "CAN he call his dog Bob?"
So the answer is, yes, of course he CAN.
Is it COMMON to do so? No, it's not common. It's not a tradition, or anything like that. But some people do, and they have the right to do so.
You mention you told your students about this. Well, make it clear that people CAN do so, but it is not a tradition to do so.