Carlin is too smart to be a true Rat. His entire routine is based on seeing through the cracks.
Which would make him a huge cynic, but I don't think he'd deny that either. He's a very wealthy cynic.
His one (weak) joke was to comment on "being [seated] to the right of Ann Coulter."
I'd bet he's a militaristic libertarian at worst.
I think you have it dead on. Hollywood Libertarians tend to drift into Libertarian camps because they are, by definition, against significant actions.