When I see pictures of SUVs in Africa, it's mostly Toyota, Nissan, Range Rover, and Mercedes? I have never seen an American SUV in Africa - except those owned by U.S. embassy emplyoees.
GM does do South African sales, I happened by one of their dealerships when I was at the World Cup. And yes, they do sell the Tahoe and Suburban down there, although thinking about it I don't think I saw a Silverado on the lot (not that I was really looking, just taking in differences really).
Most GM cars down there aren't Chevrolet either, think the guy there said they mainly sell them as the "Opel" brand. It has its own truck we don't get in America.