Are referees allowed to shake a fighter's hand?

I noticed on Bellator last night when the Russian guy won his fight, he shook hands with the cornermen and announcer but when he went to shake the refs hand, the ref refused and just nodded his head instead.

At first I thought he was being rude but then I couldn't remember a fighter ever shaking hands with the ref. Would this be some kind of rule to not show any kind of bias/friendship behaviour?

I've seen guys shake hands with the refs multiple times in the ufc

Most referees give a quick handshake or fist bump when the speak to the fighter in his/her corner before the fight begins. Once the bout has concluded, most referees are taught to fade out of the picture as a photo shaking hands with the winner could give a bad impression/arouse suspicion should there have been any controversial calls.

Kevin MacDonald
ABC MMA Officials Trainer