I don't know details, but I think Fan Duels model has had some court tests and it was ruled a game of skill (in a way that poker was not somehow) somehow because you a) picked your lineup and b) there were no random number generators.
Here's a few articles: http://www.forbes.com/sites/marcedelman/2013/10/09/fanduel-s...
http://www.forbes.com/sites/marcedelman/2013/09/03/is-it-leg...
That second one seems to specifically mention this clause of UIGEA: "1. In many cases, playing fantasy football for money is entirely legal under federal law. The Unlawful Internet Gambling Enforcement Act of 2006 includes an explicit carve-out for fantasy sports games that meet three criteria: (1) the value of the prizes is not determined by the number of participants or the amount of fees paid; (2) all winning outcomes reflect the relative knowledge and skill of the participants; and (3) the fantasy game’s result is not based on the final scores of any real-world games."
So it seems as long as the individual tournaments run have fixed prize pools they satisfy (1), (2) seems to be met because there's still sports knowledge of the sport that can improve performance, and (3) is met simply by their scoring system not having to do with final scores (and includes lots of other stats to help) although this one would probably need a text check to say what "based on the real-world scores" means exactly.