If Grissom isn't the everyday SS, he's likely going to be in Gwinnett especially if they see him as a future super-utility guy. He's played 2B in the bigs and SS and 3B in the minors, but I can remember when he was drafted the impression was he was going to grow off of SS. He's a big guy and probably not done filling out. If they see him as a possible LF, my guess is they are reluctant to have him learn the position at the big-league level.
He did okay at 2B last season, but it was easy to see that he was lacking polish, especially with his footwork. He was rushed and did well considering that, but I didn't see him as a finished product. If he goes to Gwinnett, I'd also give him some time at 1B. We currently have no one behind Olson if he were to go down.