If he is in the book, you can use him. I have a strong feeling that they left him out though, so most likely not. Basically what you see in the books is what you have access to. Older things like Storm of Chaos (where he first got rules) and stuff generally aren't legal without opponents approval anymore.
yae thats the problem my friend has the 6th edition hordes of chaos book so we dont know if its there thnx anyway