Hello Mr. Miles,
Yours is an interesting question but one might assume that if Indians learned how to use muzzle loaders more than once, the basic idea of dropping powder into a tube, followed by a ball or bullet, and ignited with a flint or cap being not overly dissimilar to the function of a paper or metallic cartridge, they would have readily taken to reloading out of necessity at least on occasion, provided that they had access to the necessary materials. I think the answer to your question is that they did, in one way or another.
Did they cast bullets or crimp them and all of that bother? Undoubtedly some did. In my first wife's family there is plenty of evidence that they did. The manufacture of rimfire brass might have been beyond the technology or most tribal Indians, but certainly not beyond their intelligence to understand, all humans being created equal according to Thomas Jefferson and others. And like many of the rest of us, it must have been a lot easier to acquire copper or brass-cased loaded cartridges through trade or some other type of acquisition than to go through the mess, fuss and frustration of handloading. After all, how many shooters today understand how cartridges are produced or the technology behind them? How many would bother with handloading if they did? Most just buy 'em, load 'em into a gun, and shoot 'em without much thought to how the cartridge is assembled or the physics involved.
At least that is how I see it. Deputy Bumpus "Mad Bumpy" Jones, formerly of Ohio and now of the Great Wild West.