Nick has some pretty good hands in MMA, but I'm not sure how well his style translates into boxing. He's effective mostly in MMA because of his volume of punches, and the angles which he throws them from. A lot of the punches that slip through the guard in MMA won't do that in boxing, because of the size of the gloves.
I know he spars with Andre Ward, but I think a guy like Vargas, even as fat and past his prime as he is now, might give Nick some problems.
Would be interesting to see.