Oh he can be, but he shouldn't be. Clark Kent is white.
There's a dozen other Superman type characters that are black that can be used, palette swapping Kent instead of elevating those characters is stupid and insulting.
There's absolutely no reason to erase a characters race that's any good. We can do better than a white character in black face.
If you absolutely need a black Superman, then we have Val Zod.
Whom, within the greater context of the Earth 2 story, is a pretty good character all his own and not just some shameless color wash. His race isn't focused on as a major trait of who he is as a person and he has some truly inspiring moments.
Hell I'd be down for an Earth 2 movie, trim the fat and you'd have a pretty badass elseworlds film. Thomas Wayne Batman, Red Tornado Lois, and even Aquawoman were pretty awesome. Power Girl had some great moments too, but she would never fly in a live action movie.