I actually think Murray can succeed in the NFL...just because the game is so different now. You can't destroy QB's anymore...so his size isn't that much of an issue when considering how little he'll ever be hit.
The biggest issue would be putting a quality O-line in front of him. The kid is much closer to 5'8" than 5'9", and throwing lanes will be vital. He played behind one of the best O-lines in the country at OU. If he's facing a collapsed pocket all the time it'll be damn near impossible for him to even see where he's throwing.
Given the right circumstances and how much the league has changed I can definitely see him doing well. Years ago he wouldn't have had a chance.