These three guys were all drafted to backup an established starter. They're not going to be part of a running back by committee, they're not going to take over the starting slot. They probably will only be part of a few plays all season outside of special teams coverage. Right now, they have zero fantasy football value. However....if something were to happen to the established starters, these three would get the chance to take over. As starting running backs for their teams, they would move from undrafted leftovers to instant fantasy starters.
Lorenzo Booker (Miami, 71st overall) - Booker likely won't see a lot of playing time backing up Ronnie Brown. New Head Coach Cam Cameron is expected to use Brown heavily this year and Booker will probably have to fight off Ricky Williams for any leftover playing time (and any leftovers). On the other hand, the odds are good that Ricky may..uh..meet Mary Jane again, the Dolphins just fired their running backs coach and there are reports that Ronnie Brown is too fat. So anything is possible.
This was taken at 20X magnification: Bears RB Garrett Wolfe
Tony Hunt (Philadelphia, 90th overall) - Hunt is currently fourth on the Philadelphia RB depth chart, sitting behind Correll Buckhalter and Ryan Moats on the bench. Starter Brian Westbrook is one of the best RBs in fantasy football, though he's never played a full sixteen games in any of his five seasons. If Westbrook goes down with an injury and Buckhalter and Moats fail to impress (which is more than possible) you may see Hunt get his opportunity.
Garrett Wolfe (Chicago, 93rd overall) - Yes, I know, everybody is saying that Wolfe is too teensy-weensy at 5'-7" to make it as a running back in the NFL. But they said the same thing about Maurice Jones-Drew last season (also 5'-7") and he ended up rushing for 13 touchdowns. And let's face it, Cedric Benson (919 total rushing yards over two seasons) hasn't exactly set the league on fire. Do you think the Bears are going to rely on Rex Grossman to move the offense during those snowy, frozen games in November and December? Me neither. I think they're going to run the ball and if Benson can't handle the load, then there's a good chance that Wolfe will see a few plays each week. I don't think that the Bears are moving to a running back by committee, but it wouldn't surprise me to see Wolfe grow into a complimentary role the way that Jerious Norwood did for the Falcons last season.