No, the NBA does in fact have a revenue sharing model in place. It is a pretty complex little piece of work and if you want to know more about it and the direct stipulations regarding anything and everything, go read this page:
http://www.nbpa.com/cba/articleVII.html
Be forewarned, it is in lawyer jargon, so you may have to sift through a lot of stuff, but it is in there.
Cheers,
Retro