Olynyk is going to play his offensive game the same no matter what position he plays and who is guarding him will be determined by the opposing team's coach. If its a center, I think Olynyk should succeed more than if an athletic PF is guarding him.
Defensively is the problem. He doesn't have the strength, length or initial leaping ability to properly defend down low centers in this league. He also doesn't have the hand speed, lateral movement, strength or foot speed to guard athletic PFs in the league.
So in all honesty, it doesn't really matter what position he plays, his game is going to be one of scoring whatever amount of points and probably giving up just as many on the other end, regardless of position. So the best scenario lies in finding a player that compliments him and allows him to minimize his deficiencies and maximize his proficiencies. If he is playing center then an Ibaka type player alongside him is key. If he is playing PF then a defensive minded center like Omer Asik, Tyson Chandler, Joakim Noah type is preferable to pair with him. Unfortunately, players like that are not on the current Boston Celtics roster.