Evaluating this from a cost/benefit point of view requires more context. If it's a brand you don't mind being associated with publicly (on the news, in blogs, in corporate pr, etc), and if you are reasonably sure you would gain something good from being there, it's probably worth going forward with.
If any of those things are less than true, adjust accordingly.
Notwithstanding the above, though, if the lawyers are already so involved that you can't walk in the door without signing a contract, how much "hack" do you think is going to be in that hackathon???
(small edit for style)