I've seen that for sale before, but it's a bit of a head-scratcher. I don't think he appears in it, but I haven't seen it, so...maybe he did. I'd be surprised if it was the Charles Bukowski. Might be a pseudonym or something.
I have not seen it, but my understanding is that he appears in one scene as a guest at a party. I don't believe he had any scripted or speaking parts, but I can't be sure. I've always been curious. I'm a bit surprised that nobody in this madhouse has seen the film.