It’s been a LONG time since I’ve read Burroughs, but I don’t remember him as being anti-racist. From what I can recall he shared the mildly racist viewpoint that was the conventional wisdom of the day.
Lord Greystoke was a superior human being because he was descended from English aristocrats. He was a gentleman by instinct, presumably genetically transmitted.
Blacks were generally background only, as I recall. The whites were both the villains and the heroes. Russians and Frenchment, in particular, seemed to inherit villainy.
But it’s been a number of decades, so don’t quote me.