So now we know straight from the source that Xehanort wanted to find Ven in the Chamber of Waking at Castle Oblivion. I say that because I remember some people speculating that Terra still lived in Xehanort and that Terra wanted to find Ven.
But why would Xehanort want Ven? Did he want to use him as a vessel? It'd be much easier considering that he actually has no heart within him. I don't really see any other reason though. Besides, Xehanort didn't show any interest in Ven except for the creation of the X-Blade since trying to use him like he used Terra didn't turn out right.