Poy can still be a serviceable NBA player. The problem Poythress has is that he is an NBA small forward, but he doesn't have the basketball skill to play small forward. He has the athletic ability, but his dribbling and shooting are not good enough for him to be a real threat at small forward. I believe that Cal tried to develop him as a small forward to prepare him for the NBA. Had he been prepared as a power forward UK would have been a lot better off and it probably would have fit Poy's basketball skill better. However, it may not have been best for Poythress long term.
Cal has attempted to get the best of both worlds out of Poy on offense by putting him at the short corner. This allows Poythress to step back and shoot some threes and play like a small forward at times, but also allows him to get the ball on the short corner and take the ball to the basket with one or no dribbles. Playing there also allows UK to take advantage of Poy's best asset, his athletic rebounding ability. Having Poy rebound from the short corner gives UK a lot of offensive putback/dunk opportunities.
I think the best way to utilize Poy at the short corner is to play pick and roll with a big man. Skal and Ulis would be good here. Skal picks for Ulis and rolls and there is a shot opportunity for Skal (much like UCLA got with the big white kid). If Ulis sees the hole then he can drive, which will often mean that the man guarding Poy will have to step up to stop Ulis. This leaves an open lob to Poy, or a little dump pass to Poy on a short cut. Either way it leads to a dunk for Poy, which is his best shot (haha). Where UK will struggle with this, and in turn Poy, is when opposing teams play zone. That is when Poy will have to actually hit a few jumpers from that short corner. If he can do that then he can loosen up that zone and help the offense out a lot. So far this year Poy has struggled shooting, so I hope that improves.