I just watched the scene. I don't think it's him, although the raspy voice is similar. The nose is not his. George C Scott had a very prominent nose, that was never "fixed". The guy in the production booth has a completely different nose. But I agree the role is played by an insider - perhaps, the show's real life production booth operator.
The hired killer in the black and white movie, "The Professional", is indeed the show's director, James Frawley.
Yes it was George Scott in Requiem for a Fallen Star. He is in one of the scenes where the movie star character is shooting a movie. He is holding a script of some other paper. In reality GCS was married to the co star of the episode, the actress who played the assistant. I think her name was is Pippen Scott.