In one sense, Dilbert is quite often not funny at all. It is just absurd and somewhat familiar to office drones like me. We recognise certain situations and we wish we could handle them with the boldness, callousness or rage depicted in the comic strip. Does that make it more of a catharsis than comedy? I think so.
Mokalus of Borg
PS - Scott Adams' own theory of humour would suggest Dilbert is meant to be funny on the Recognisable and Cruel dimensions, and maybe Clever and Bizarre.
PPS - To me, it might not be cruel or clever enough, or too bizarre.