Were there any real black people in this movie?

That's a stupid question as anyone can see they are Japanese. Furthermore, some of the "natives" wear no make-up at all, but are seen as Japanese women.

As authentic as Mickey Rooney in Breakfast at Tiffanys!

Don't know where the island was supposed to be, but Okinawa is an island in Southern Japan and Okinawans are Japanese (at least in citizenship, they consider themselves Okinawan). They are quite a bit darker than Japanese from the mainland (in fact, the Japanese aren't kind about the pigment differences). Due to thousands of years of the Japanese (and other Asians) sailing to the island, kicking butt and raping women, they do appear more Japanese than some more Polynesian people.... but why do you think Hawaiians have Asiatic features?

Japan has no interest in racial diversity in its movies