Ven's heart isn't in Roxas, I think I remember Nomura saying, Roxas' appearance was just a side effect of Ven's heart being in Sora. He did say "It has been assumed Ven's hear is in Roxas' or something like that, but he was refering to the speculation among fans before BBS was released i think.
Ah...okay. So I didn't misinterpret what you said.