We need to be less essentialist about this. Orcs are Orcs, they don't resemble Native Americans (or any other ethnicity) all the time. In fact, because of what they are, they might resemble different ethnicities as different times and in different uses.
As I said earlier, the issue here is essentially structural. D&D is extremely American. One only needs to compare it to Warhammar, a British game, to see some of those differences. D&D tends to assume big wilderness areas and frontiers and keeps on borderlands. This may not be universal, but it's common. Take for example the North in Forgotten Realms the 'Savage Frontier'. It clearly is influenced by ideas of the North American frontier. And part of the narrative structure of stories of the frontier is the savage threat beyond the frontier. Orcs (and other monsters) fill this roll in Forgotten Realms. Reavers do the same in Firefly. This doesn't mean that Orcs necessarily have Native American characteristics, they can fill that role without feathered headresses or rain dances, or scalping or whatever other stereptypical idea of Native Americans is in the culture. But when people recognise this structural role, it's very easy, if they're careless, to start adding in those ideas as well.
And if you're setting is consciously not North American then you might start looking for other details to help flesh out the Orcs in their structural role and suddenly your Orcs are Mongolians or Zulus, or Saraceans or something else.