This is GREAT news! Jimmerson is an outstanding find for sure. He was one of those guys who when you watched his team play, you thought "surely they'll give him the ball more" type of deal. Anyway, great body for an RB, good athlete, and will be a nice player.
Nothing against Brandin Byrd, but the Jimmerson-Whitfield combo is VERY exciting to think about. These two are as impressive as LD was out of Haltom on video (not saying they'll develop like LD, but it's a good time to be optimistic). My guess is that Canales will ask Byrd to add weight and become more of a short yardage/between the tackles guy.
Of the 3 young RB's, Whitfield will be more of the homerun threat/get to the edge guy, Jimmerson is good inside and gives you the ability to do some things in between the tackles as well as on the edge, and Byrd will probably be utilized more between the tackles. Nice collection of young talent for Coach Grant. Now we need to get him some U-Backs and H-Backs.