Chris Dickerson and Jim Morris, who of course are black, won the 1970 and 1973 AAU Mr. America contests respectively back when it when it was under Hoffman's control. Dickerson, in fact, was the first African American ever to win the AAU's Mr. America title.
Nevertheless, Hoffman was indeed a racist, a political reactionary, and as generally shady in all his dealings as the Weider brothers ever were. That--and Hoffman's at one time very successful magazines--is probably why the Weiders detested him so much; they realized he was even more of a scoundrel than they were.
The full story of Hoffman's York empire and its primary influence on the era's iron game is fasinatingly told in John Fair's masterly "Muscletown USA: Bob Hoffman and the Manly Culture of York Barbell. It's in paperback from Penn State University Press, and last I looked it was available on Amazon. For my money, it's an essential book in bodybuilding history.