I've been going to camps down here for years, and I've found that 1-on-1s are very predictive of man coverage skills in college. You can't see tackling and recognition skills, zone coverage, etc., but you find out which guys are physically and mentally capable of playing man at the next level.
Quincy Wilson is the best example. He was lights out in 1-on-1s at camp but sucked as a senior on the field. His man skills ended up carrying him to the second round of the draft.