Anyone can make an OT for something and no one has dibs on anything.
We have a thread for people to coordinate to avoid situations where two people might be interested in the same OT. It's called the |OT| |OT|:
http://www.neogaf.com/forum/showthread.php?t=450653
Our expectation in that case is that anyone interested in contributing is allowed to work with people. If people can't agree on working together, then they all stink.
Our typical policy these days is that |OT| threads should go up the day before release for games and within a week before release for non-game content--this is basically a policy to prevent the first 50 pages of the OT from being hypegasm "OMG NICE OT" no-content posting.
Sometimes when an |OT| is made for something related to an existing community, people organize in that community. For example it would be typical for people working on a Steam Sale OT to organize in the Steam community, or people making a Superbowl OT to organize in the Football threads.