...another stamp that has not aged particularly well, in my mind, is Scott 565....But in the context of that series? Up against all those specific past American leaders ... a ... Native American?
Seems that there is no problem with a Native American, the 8th such elected to the US Congress, "up against...(an) American Leader (POTUS #43) at the same podium:
...to regard American Indians more as a natural wonder than as actual individual people.
Well frankly some are both natural wonders and individuals. Two quickly come to mind, Senator Ben Nighthorse Campbell, 1964 US Olympian and Jim Thorpe, 1912 US Olympian, Gold, Pentathlon and Decathlon.
In politics Ben was instrumental in establishing the National Museum of the American Indian on the National Mall. It is there you can learn about Chief Hollow Horn Bear whose portrait likely appears on the 1899 $5 silver certificate (or it was Running Antelope who died in 1896) and the US 1970 $10 Military Payment Certificate. As to the 1922 stamp, he could be pictured as "generic" but not by name as he had died March 15, 1913 thus was not dead 10 years as was required for non-Presidents appearing on US Stamps.
Portrait photo of Hollow Horn Bear-
Color lithograph derived from portrait-