Sora was a heartless.they are both heartless...
Xehanhort not so much.
He casted away his body and and that turned into Xemnas, but his heartless isn't really a heartless. At the time that would be the easiest thing to call Ansem the Sod.
Sora did become a heartless, but Kairi cleared the darkness around his heart and he returned. But since Roxas is Sora's body how can Sora stand and walk like a normal person? Only his heart remained.if that was true then roxas wasnt really a nobody,
She might not beneither is namine.
lol nobut then again you might go along with the theory of roxas having ven's heart