To an extent. If there aren't many black actors being cast in Shakespeare, then having a white actor blacked up as Othello is surely an issue?
Talk to Laurence Olivier and Orson Welles about that.
Personally, I think actors are paid to pretend to be somebody else and, provided it doesn't affect the audience's suspension of disbelief, I think anybody should be allowed to play anybody.
That said, I saw the Welles production of Othello while I was at school - it was one of the set texts for O levels - and I found the black-face distracting even back then, so it's probably not a good idea to have a white actor play Othello.