Marc Ambinder reports that Black told him "as he has told other reporters, that his firm ran every potential foreign client by the State Department and/or the White House in whatever administration was in power and asked whether the scope of the work fit with American foreign policy goals." He also quotes Black as saying he's "not ashamed of anything the firm did."
There's no question that helping the Mobutu regime in Zaire was something the American governments of the time were okay with. But anyone who had anything to do with aiding Mobutu and isn't ashamed of it really needs to get his conscience replaced. I highly recommend Michela Wrong's book, In the Footsteps of Mr Kurtz: Living on the Brink of Disaster in Mobutu's Congo. American support for Mobutu was an enterprise that involved a lot of people over a long period of time, so Black's hardly the only one with something to be ashamed of, but he really ought to be ashamed.