To be honest, I think it’s been hinted that they’re personified, but given how extremely careful and informed you would have to be
in portraying them accurately and respectfully, I don’t think it’ll go any
farther from there.
It would be hard to
fit them into Hetalia given how everything is based off stereotypes. I say this
because of how atrociously these peoples have been treated as a result of
negative stereotypes. Applying more stereotypes just doesn’t seem like a good
idea. If at all, I think it should be more of a matter of self-representation in the
fandom if those coming from these cultural backgrounds feel the desire to share
their customs and ways of life. It’s a tricky subject and should be taken very
seriously.
As for your headcanons? I’ll get into this in another post,
but we’ve seen how the nations are often forced to do things they don’t
necessarily agree with. It’s sad, but true. Also, yes! It would be quite the scene
to have all of them personified.
But, as I said above, there are smalls hints and clues in
the strips that make me think that Hima is alluding to their personification.
First, you have the French-Indian War in America.

That looks to me like an Indigenous personification, as in other
panels that reveal the different sides of each war depicted by Hima, it’s
almost always the nations involved save for the occasional leader here and
there.
There’s also the fact that in “The Battle for America”
America is referred to as more of an “ingredient.” How I interpret this is he’s
simply part of the land at that point. If America’s the ingredient, then
perhaps that’s Hima subtly acknowledging the fact that he’s not the whole of
America. He could have represented the early settlers and then later adopted
the full representation of the land.

This doesn’t mean to say that the Native tribes aren’t
personified themselves, though. They organized themselves differently from
Europeans, so a tribe or band would likely be their equivalent of a nation.
We’ve also seen with Japan’s prefectures and China’s provinces that it’s not
only just the whole nation personified but parts of it as well.
Overall, I don’t think Hetalia is quite the right medium to portray
them. For one thing, their histories are not accurately depicted in the first
place, and on the other hand, Hetalia isn’t the most historically accurate
series either. It just doesn’t seem like a good match.