[Zigûr]

The ones that appear in the film are meant to be the Dunlendings, wouldn't you say?

Oddly enough when I think about it, they don't seem to appear outside of agreeing to serve Saruman apart from perhaps a couple of scenes of raiding in Rohan.

One thing I've always liked about the book depiction of Saruman's armies is the seemingly rather eclectic nature of his forces: Dunlendings, Uruk-hai, lesser Orcs, and wherever the "Half-orcs" existed in that scheme. "The Battles of the Fords of Isen" in Unfinished Tales gives a particularly good sense of that, I think.