Battles of the late Third Age

[Kuruharan]

troops maintained solely by Saruman...Perhaps some were even desceded from the old Gondorian garrison of Orthanc.

I think considering their weapons they would almost have to be Saruman's Own Pike Regiment. I always pictured them as being human. I never really considered where they came from. However, they were evidently not numerous because they are never mentioned again (although that is evidently where Jackson got the idea). Their lack of numbers as well as their equipment makes it appear to me that they were probably some of the old people of Isengard who had lived there for generations.