Well I remember reading that GW stated that Russ never had the wulfen issue himself. But then you could say the warp did it, khorne does love canine monsters.
And I remember reading that the space wolves in a hunt for Russ, found his armor in a chaotic shrine. Could there be more truth to that blurb than we imagine?
But this certainly would play into the rumor of a loyalist going traitor, and a traitor going loyalist. Even if i think noone would expect Russ to turn as he was the most loyal of them all. Perhaps thats why he might be targetted to be the one turning? Who knows.