Does a SS theme require approval from the SS company? I imagine it does (haven't checked on this) before being posted to the themes area of the SS website, but I am assuming that anyone with the ability can create and post (even sell?) SS themes anywhere s/he wants to post them?
We do review submissions (just like modules, widgets) just to check they install / work and contain no viruses or other nasty embedded shocks and yes anyone with a member account on this site can submit themes.
If you wanted to sell your themes we don't have such functionality on this site so you would need to setup your own premium market place.