It would depend on his opponent, how they plan their defense and offense... how they would study his style... weakness and strengths.
I don't think he would get completely dominated, nor do I think he could come out winning. He would hold his own, but his style is strictly stand up and he would have to be on his A game and score a knock out quick or else. If his opponent did his homework... his goal would be to get tyson down and in a postion he's not familar with... (thats if his opponent is strong in ground defense).
He has plenty of street fights to back him... but he's still a dirty fighter and MMA and UFC as well as Boxing have some rules... and Tyson just has an issue with these rules. He is and always will be a dirty fighter... caught or not... and I don't discredit his ability due to that... he's street smart and really talented all in one nutshell.
If he obides by the rules of the federation, and is put up against someone with a MMA background... I'd opt for someone dominant in ground defense... I couldn't see Tyson winning. If he were matched up with someone that was more of a standup fighter... that guy better have some back up plan! Tyson is an OX, strong and very aggressive... his aggressive nature can play for him or against him.
I'd like to see him give this a go... It would prolly be a huge money maker for him.