Roach is hardly a fraud, not going into that in an MMA thread but that accusation usually comes from people who can only name Pac as a boxer he's trained.
Anyway, I'm not saying GSP would be wise to try outbox Bisping by any means but at some point he's going to have to and having Roach advise you about your boxing and what you're doing right/wrong is a positive to me (yes I know this is MMA and not boxing), regardless of anyone else's view on Roach.
But like I said, he's obviously not going to be looking to trade in the pocket all night but he's not going to be landing takedowns at will so there will be numerous times he has to trade.