Before the Internet, when it was harder to have tons of varied information on your (physical, wooden) desktop, an old writer's trick for naming foreign characters was to go to the Atlas or a globe and pick a place name from the relevant country.
That way you had a name at least plausibly related to the desired ethnicity, something you might otherwise have a tough time dreaming up.
Anyway, I never heard the Zulu story. It was always my understanding that Sulu (Sea) was picked off the map because it was Asian but not specific.
Incidentally, in the version of TOS dubbed in Japanese, Sulu is changed to Kato. And Scotty becomes Charlie for some reason. And they made up their own stories, and Kato was kind of the boss.