I think you missed the other way. If you have a large community and want to sell community related merchandise then you would want OSC to be a secondary software to vbulletin. (ie. you would want vbulletin to be the main software with OSC integrated into it instead of vbulletin integrated into OSC.
By the way, I am just looking for a way to put vbulletin header/footer on the OSC page without using iframe. That way I can have specific title/meta info while still maintaining a seamless visual integration. If anybody succeeds please post up
Mike