Oh, yeah. They confirmed it a few months ago. Fourth episode of the new season, called "Cure". He will be playing Dr. Curtis Knox (CK again!) who may or may not turn out to be Vandal Savage.

Actually, that's the only reason I'm still watching this damned season. It's about TIME he was invited. mad I kept hoping that maybe they would sign up Teri too, but that one failed to materialize. grumble

“Is he dead, Lois?”

“No! But I was really mad and I wanted to kick him between the legs and pull his nose off and put out his eyes with a freshly sharpened pencil and disembowel him with a dull letter opener and strangle him with his own intestines but I stopped myself just in time!”
- Further Down The Road by Terry Leatherwood.