That would count as proof to me. I'm in Ohio and when I got divorced (no fault) we didn't need evidence or reasoning. But there was an option to "blame" the other person (e.g. alcoholism, domestic abuse, cheating, etc) that is why I was curious if he had any sort of proof. I recommend checking Michigan's divorce laws and see if there is an option for that.
My advice would be to have him talk to a divorce lawyer asap. If he has proof and whatnot, I'm not too sure about Michigan laws but they would be his best resource
