I had a notion in another WI asking about the formation of Indian states in the USA. One (of many) obvious problems being that no distinct, particular Native American nation amounted to a population comparable to a US state. It is very difficult to judge the truth of this impression before the 20th century to be sure since there were no reliable censuses of Native peoples, whereas of course in 1776 the smaller colonies joining the revolution were small indeed!
However it did seem evident to me that if all the Native American peoples (known in such a low-probability ATL as this as simply "Indians" of course) were grouped together, then their numbers would fall in the ballpark of a US state. I postulated a visionary (to speak kindly of myself) notion of an Indian Confederation which would group all tribal territories, scattered about the growing USA, into one political entity of equivalent status to a single US state--they'd send two Senators to the Senate and a number of Representatives to Congress varying from just one to however many would be proportionate to their total population.
Getting such a thing started would be the big hurdle. Of course keeping it in being despite strong interests wanting to take it apart would also be tough, and especially so in the face of dissensions among separate Native peoples all grouped together like that--every tribe's most mortal traditional enemies would of course be included.
Handwaving it into existence and persistence though, I figure the longer it does last, the more integral to the US system it becomes. By now, such a Confederation would presumably hold a great deal of US land, notably in the west, and have a medium-small population ranked among states, somewhere around Tennessee IIRC.
If we had a TL where such an institution existed, I would think that despite Anglo chauvinism about superior Euro-Christian ways, a great many elements of Native culture would indeed transfer over to Anglo culture, particularly in politics. The Confederation would be in some ways a microcosm of the Union as a whole and all sorts of issues might be resolved there to serve as examples of how to do it on a national scale.
The trick, again, is to get it started, and I suppose the focus of your question is on the pre-Revolutionary period. If certain Native peoples and colonial governments had evolved extensive formal relations, producing individuals who identified as belonging to their people but moving in respectable colonial circles, became the face of their peoples, and these peoples were not just in one region but several, and they formed the notion of a collective federation of Native peoples who would seek to bring all Natives under their collective bargaining wing, and finally a decisive majority of these worthies resolved to lead their respective peoples to support the Revolution in return for formal recognition of this collective body representing all Indians who submit to the United States, then you'd have some grist for your mill right there.