The Israelites originate in what's now the Shatt el Arab, the river formed at the confluence of the Tigris and Euphrates rivers. So no, no sub-Saharan African mixture, at least at the origin. On the other hand, Israel is in Egypt for a heck of a long time, between 250 and 400 years, according to various perspectives. Egypt is not a sub-Saharan country, obviously, but there was a lot of to-ing and fro-ing with Nubia and Ethiopia, and I have to assume that the same thing happened to the Israelites that happened to Africans and Europeans in the Americas, perhaps to a lesser extent but mixing I have no doubt took place.

All of that has probably nothing to do with the representation of the text in the program, though. Race-blind casting is pretty much the norm in the theater, anyways, although not quite yet in Hollywood. I remember when Kenneth Branagh directed his version of "Much Ado About Nothing" and decided to cast Keanu Reeves and Denzel Washington as half-brothers. No biggie, as my brother in law used to say.
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