Antoine Winfield is not only fine with lining up against the slot man, he actually welcomes the opportunity:
I love the slot. You get more action, the chance to make more plays. A lot of teams throw the ball to the slot receiver on third down, so there’s just more opportunity out there.
Vikings D-coordinator Leslie Frazier may actually prefer letting Winfield play against the slot-man, since Marcus McCauley is perceived as being better on the outside. Problem is, McCauley is far from having the nickelback spot locked down, but is facing fierce competition from Charles Gordon and Benny Sapp. Winfield would likely have to stay on the outside were Gordon or Sapp to win the third corner job.