Olympic Sprinter on the Patriots?

Can this guy really play in the NFL? 

Last week the Pats signed free agent Jeff Demps, a former University of Florida Gator and member of the USA silver medal winning 4 X 100 meter relay team.  He'll practice for the first time tomorrow.  My question is this: if a guy is a serious NFL prospect, and he literally has "world class speed," how does he go undrafted?  Obviously there is much more to playing football than running fast.  You have to put on pads, stop, start, change direction, and accelerate quickly; not to mention sustain bone jarring hits from very large men.

At Florida Demps returned some kicks, caught a few passes, and was a part time running back as well.  But can he actually do any of those things well enough to play for the Pats?  I hope he makes the New England roster, and if he does it could be a great story to follow.  But, my guess is he won't make much of an impact.  Scouts say he has average hands, and he is definitely undersized (5'8" and 185 pounds or so) for an NFL running back.  At Florida his yards per carry dropped each year (from 7.8 as a freshman to 5.8 as a senior), plus he hasn't done anything football related since the Gators bowl game last January 2nd.  And now he's got less than two weeks to try land himself a spot on the Patriots.

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