I really don't know anything about these folks, except for what I've read, but I believe that they're probably from the Thao Tribe. Sarj says that the gentleman wearing the tie in the first two photos is the tribal chief and this website has a postcard image of him wearing traditional dress (click on the small image to enlarge it).
I'm always fascinated by claims of land ownership around the world because it really depends on which baseline one wishes to pick, doesn't it? Today the People's Republic of China refers to Taiwan as a "renegade province" of the PRC, when in fact it has never actually had ownership of the land. Han Chinese began emigrating to Taiwan sometime in the 1600s, but (as far as I know anyway) it was never a province of mainland China.
The ancestors of the native people shown in these photographs probably have a more legitimate claim to Taiwan because they arrived there as early as 6000 years ago. But as the above link points out: "Archeological findings indicate that Taiwan had been inhabited by other people before the current aborigines came. However, little is known about them, particularly when and why they disappeared."
So even the "native" people of Taiwan weren't the first to reside there. It all depends on where you want to draw that line to claim ownership.