I've watched a ton of Scotty Hopson.
First of all, he's not a combo guard. He's 6'6"-6'7" but not really strong enough to deal with SF's on a full-time basis. He has length and great hops, and if you search YouTube you'll find several highlight reel dunks. When he's aggressive and decides that his matchup can't guard him, he's capable of really pouring it in - he has a high release with a rainbow arc that is unblockable, and he's capable of getting hot from midrange. He's a poor dribbler for a guard but his athleticism makes him effective on straight-line drives to the basket. He's not strong enough to consistently finish through contact, but his athleticism will allow him to finish some pretty acrobatic plays - or to just go straight over the top of the defense.
At Tennessee, he typically displayed poor effort in every area of the game except scoring. He won't rebound much, isn't a good passer and is typically ineffective on defense (although his length will nab him the occasional steal). He's prone to sulking on the court - if a call or play goes against him, he's prone to pouting and will subsequently disappear for long periods of time.
He's not a leader, but he's a good kid - no off-court issues at a program that was sometimes rampant with problems. I really think one more year at school would have done him a world of good. Tennessee has a new coach who has a history of demanding that his players give him full effort in every phase of the game, and I think a dose of discipline would have been immense for Hopson's future.
For the Celtics, I don't really see him as a good fit. I don't see Hopson providing anything that we couldn't already get from Von Wafer, and after this last year I think Wafer is probably superior in the other areas of the game aside from scoring. He has more potential than most juniors out of college, and a disciplined team where he is allowed to grow and make mistakes could do wonders for his eventual productivity. I see him as a benchwarmer at present, with the potential to be an important piece of a good team if he figures it out.