Fair trade?

If you need pitching, don't do it. On one hand, you'll get one of the premiere SS in the game in Rollins and Guillen is playing 1B this year anyway. Also, since you are only using Dunn off the bench, you are not risking too much with him. The kicker is that Cole Hamels is an excellent pitcher. Just because he has a losing record (2-3), it is not an indication of how he has pitched this year. He has a 2.75 ERA and has 30 strike outs so far this season. He will be a work-horse for you as a starting pitcher. Do not make that trade!