Why on earth should it not be OK for black people to use the service? And what is so "white" about it? Because black people are supposed to be activists and believe in identity politics? I follow plenty of black people on Twitter who don't belong to that crowd.
Have you ever wondered if is ok black people to use Hacker News? After all, it was created by white people? (I don't even know the skin color of the creators of "Unwoke.hr" - why do you assume they have to be white?).