According to Kotaku's Owen Good, NBA 2K12 Legends will not be available online.
Quote:
None of the 34 teams unlockable in "NBA's Greatest" will be available for online multiplayer modes. There had been some confusion, even hope that they would, as earlier reports suggested that once a team is unlocked from "NBA's Greatest" it is available across all modes of play. 2K Sports just confirmed for me all the modes in which these teams can be used, and online multiplayer isn't one of them.
I don't recall Ronnie 2k or any other 2k developers or 2k marketing team ever saying or confirming or promising that there will have an online insight this year. Of course I could be very wrong about this so my apologies in advance if it has already been confirmed.