You don't have to directly interact with, know, or coach a player to have an opinion on whether or not a guy will go pro. You can get a good read on a guy's abilities simply by watching him play in games over the course of his career.
I feel bad for Shy because of the injuries he's experienced while at Tennessee, a couple of which came on a very questionable (at best) hit during the Georgia game a few years ago. When he's played, I think he's done OK considering I don't think he'll ever be the player he could have been. I wouldn't put him in the underachiever category like most of the defensive line teammates he's had over the years (McKenzie, Phillips, Kongbo).
I think he'll have to wow people during workouts/at the combine, which might be difficult given his injury history to get a shot. The injury history itself will scare a lot of people away. He's missed a lot of games in his college career and when he has played he doesn't exactly dominate games or obviously make is presence felt.