I agree completely that Matt Hamill with a functional ground game is a major threat to the LHW division, but the problem is whether or not he'll actively use it. As we saw in the Rich Franklin fight, he has problems following his own game plan as well as his corner's advice. His trainers weren't too happy about that and subsequently bitched him out in some interviews.
He's an incredibly wrestler who can almost certainly take down anybody in the division. If he starts employing this tactic, his best asset, I think he'll give the division tons of problems, BJJ or not. With BJJ, forgetaboutit.