Have been working on the piece, but just returning to mention something about the original. I have a theory (unproven of course) that the Riffs in TDS are actually inspired by the Sahrawi people, and the tribe that appears in the play are inspired by the Oulad Delim in particular, for two main reasons:

1) RL Riffs aren't Arabs, but Berbers, as Q said, and their traditional territory isn't anywhere near the desert (which makes up only the southern part of Morocco).
2) The area of the operetta's Riffs' territory is specifically said to be under French control. French Morocco never included the north of the country but it did include every other region, including the south.
3) The Oulad Delim mostly live in cities like Dakhla in the Western Sahara, but there are some in Southern Morocco, and they were opposed to the French.

Of course, all this assumes that Hammerstein knew about this. He and the other librettists probably took some real-life inspiration and made up everything else.