1. In my opinion, the NFL's "three years out of high school" regulation cannot stand up under legal scrutiny. The problem here is that the regulation does not accurately correlate to any rationale they might present (the safety of a young player, for example). If a young kid misses two years of school due to illness or something like that (or because he is just not very smart at all), then he may be finishing high school at the age of 19. According to the NFL's rules, this kid would not be able to play in the NFL until he is 22 years old, which is two years later than other "normal" players would be eligible. Conversely, a bright young kid who was somehow able to finish high school by the age of 12 would be eligible to play in the NFL at the age of 15.
2. Any terms of the league's collective bargaining agreement would be irrelevant in this case, since the CBA clearly cannot apply to players who are not members of the NFL Players' Association.
3. There are actually two separate issues here, related to the same case -- a.) whether the NFL's restrictions represent restraint of trade from Clarett's perspective, and b.) whether the NFL's restrictions represent a restraint of trade from any one team's perspective. Clarett's best legal strategy here is to make the case that an individual NFL team should at least have the option to draft him.
4. In this case, the NFL should not be considered an "employer" in any sense. Individual teams are employers -- the league itself is not. The only evidence you would need to confirm this would be a player's income tax return. The teams themselves pay the players, as well as any of the costs associated with paying them (FICA taxes and other payroll taxes, for example). The NFL isn't exactly a "franchise" company like McDonald's, either -- it actually functions more like a "pro football cartel" than anything else.
5. Anyone who is certain that the U.S. courts would side with the NFL in this case should go back and do some research on the infamous "collusion" case involving a bunch of Major League Baseball players in the 1980s who successfully sued MLB on the grounds that a group of owners conspired to refuse to tend offers to them when they were free agents. Interestingly, this represents an interesting potential future legal action against the NFL if Clarett is actually declared eligible for the draft but is not selected.
6. Regarding #5, he would never go undrafted anyway -- Al Davis would select him.