No he's not. I know this since I actually got to attend a week ago one of his shows and sat in the audience, stood 1. read more
Also if you watch episodes online you see shots occasionally of the audience and once and a awhile Stephen Colbert will address his audience. Heres some photos below for extra proof, I got from Google, the first one was from a news article talking about Stephen Colbert’s captain America shield I think but it also was a great shot of the studio and the audience in one. read more