I’d wager that if you look at black graduates with degrees in real disciplines like, business, science or engineering, their employment rates are on par with the rest of the population. Minorities who can’t find employment often majored in ethnic studies where there is only room for a few Ward Churchills and Lamont Hills to make their mark.
Also throw out graduates of "traditional black colleges" and I'll further wager that black graduates of mainstream colleges with the degrees you mention have probably even higher employment rates than the norm. A big chunk of corporate America is quite concerned with being "diverse," and therefore are willing to go after qualified mainstream black graduates with a vengeance.