He is not a comedian, more like a fashion, lifestyle and relationship expert. When he says that men should learn to say "shut up, bitch" it is not intended as a joke but as legitimate relationship advice. His viewpoints are well known, and Dell got exactly what they could expect. What is surprising is that Dell thinks this kind of relationship-advice is appropriate entertainment for a business conference.
I wouldn't go as far as saying he's explicitly known for making racist jokes. He is however known for (and markets himself as) being politically incorrect - which may very well include both racism and chauvinism.
He did get into trouble for saying that "some negroes do look like monkeys" on national radio. But generally he is more known for controversial relationship advice and armchair heroics.
There was also that controversy last year when he said Breivik would've killed fewer people if Scandinavians weren't so passive, and were more willing to fight like Americans. I'm surprised that after that kind of press, corporations wouldn't steer clear...