Considering Brian and Mike still aren't talking to each other, singing together is probably a bit much. Although i'm pretty sure it's Mike who's going out his way not to patch things up.
Still, Dennis did marry his daughter so i can sort of see why he's still pissed off. But it's not as if Brian was forcing Dennis to marry her. I've always seen Mike as an arrogant prick anyway. The guy doesn't like Pet Sounds for god's sake!
Plus it could be argued that if he hadn't constantly been putting Brian down, having a go at him for his "ego music" then maybe Brian wouldn't have gone insane or whatever. Although I will admit if there's anyone to blame it was mainly Murry Wilson, i still think that if Mike had been able to understand Pet Sounds and Smile then maybe things would've turned out a lot better for Brian.
Bruce kicks ass though.