I'm pretty positive on him making the 51 man roster. If nothing else, it's for his change of pace. Maybe we'll see him just 4 times a game, but he's one of those guys that has the potential to break away on every play.
Like you said, blitz pick-up might be a problem, but his hands are very good. Doubt that he can replace BJ as our 3rd down back, though.
Biggest problem that I can think off is that he's lacking amazing speed. He is very quick, agile, has great balance and can pull of some moves, but he doesn't have that break away speed.