1)  No, they did not create a partnership.  If they had, the players would have every right to see the books.  But they didn't. 
  
2)  The players are employees; as others have said, the owners' financial affairs are none of their business. 
  
 
  
  
 
  
The NFL dictates the terms and conditions of employment.  At the early stage of a player's career, it's a take-it-or-leave it proposition because generally, a player must play for the team that drafted him or not play pro football at all.  (Very few players can Elway themselves to a new team.)  Later, the NFL still dictates just about every non-salary term of a player's contract.  Because there is no real competition, the players are invoking the antitrust laws.  This doesn't mean that I see any merit to their suit, btw.