Riku 5234: Heh. You might want to reread your own first post. If Ven's heart took over Sora's Nobody, creating Roxas, then regardless of weather Roxas is Ven or not (Sorry about the disclamer: I've seen too many flame wars elsewere on this subject), when Roxas was reabsorbed into Sora, so was Ven's heart.
In short, based on your own arguements, and barring something in KHIIFM+ that I missed, Ven WAS in Sora.
Edit: Now, if you were talking about the second half of the first KH or CoM, than yes, Sora was flying solo.