If I remember correctly, an interview about the RBN stated that for the submissions on the RBN to work, each submitter would have to be set up as their own vendor. At the time, that was stressed as a major hassle, but the more I think about it, a long, drawn out process is much better than having the system without RBN support. And looking at the actual submission to become a vendor http://www.vendorportal.sel.sony.com/ , it doesn't look as complicated as it was said to be. As far as audition mode is concerned, the PS3 already supports computer-generated-user-created files, such as custom themes, or mods for Unreal tournament III.
I'd say there would be plenty of PS3 users, myself included, willing to go through the process of setting up a vendor account if it meant that they could author for RBN