I don't think Ven IS Roxas. Certainly they have some connection, but BBS is set 10 years before the first KH. So that would make Ven/Roxas like 30 years old by the second KH. So that doesn't really work.
Huh, I always thought that Axel was Riku's nobody....because Axel was really good friends with Roxas, who of course is Sora's nobody. So I thought that bond was created because of Sora and Riku's friendship?