So Beck appeared on The Onion's show and enjoys it.
So what?
It's not like conservatives boycott anything liberal. MAD magazine itself (that I compared The Onion to) is liberal, and it's still a cultural institution, and a magazine I've enjoyed for decades (I have scattered issues from the 50's and 60's, and a complete run from 1970-1977).
Beck, O'Reilly and other conservatives regularly appear on liberal programs. Pat Buchanan has been a commentator on MSNBC for the better part of a decade. They still espouse a conservative viewpoint. And in Beck's case, with a considerable sense of humor.
I actually haven't watched Beck since he left Fox at the end of June, and may or may not subscribe to his gbtv.com network at some point.