As for licensing the software, I think that's kind of missing the point. Anyone can develop equivalent or better software pretty easily. What people need is to be able to trust the site's operator not to run off with their coins, and not to play against them using the server seeds. That "trustability" is not something that can be licensed out.
Which is an argument for open-sourcing the code. No sense is having two people write the same code twice.
Although it might give you problems if someone sees a Just-Dice replica and trusts another users with their coins, thinking that the JD software makes their coins safer.