Very nice! Chess has always been a powerful metaphorical engine. So has baseball. The pitcher-batter relationship is often described as a chess match. It makes sense to me. However, I'd never thought of extending the metaphor as you have. Nice job.
I like your categories and associated attributes. We had many similar picks in the back ranks. Pawns not so much.
On reflection, I think the assignment of King and Queen roles by position should be swapped. While Babe Ruth as a Queen has some gender bending problems, it is hard to imagine containing all that offensive power in a chess King. A pitcher, on the other hand, is seldom an offensive power yet central to the game, very much like a King. Also, aspects of "getting to the pitcher" translate naturally into the chess metaphor. Otherwise, I like your thinking.
I'm going to try coming up with a set for the 2013 season by league (using my King/Queen switch). The back ranks are pretty easily populated. The pawns, once again, are less obvious. I'll get back to you with my picks.