I can see this one perhaps heading for the courts, but of course it probably won't happen until well after this year's big event is over and done.
See article here: Tailgating Forbidden On Super Bowl Sunday (CBS4 Miami original article)
As noted in that article, no law is known to forbid tailgating at Dolphin's stadium, but that isn't stopping the No Fun League from denying the people that want to take part in the traditional football Sunday festivities (tailgating) the opportunity or right to do that tailgating. The N.F.L. is of course claiming it's all for security reasons and that may be true, but getting away with a ban for a distance of as much as a 1 mile radius around the stadium would seem to mean they are going well above and beyond anything that they'd have the right to do.
Unless the N.F.L. has paid a considerable price to all private property owners in the area, I don't expect that they'd have much right to do anything there. Of course they may have done so, and if that is the case, then they can govern over the areas they are paying for as they see fit -- even if it means they behave like NAZI's in the process.