Well, I would say that if the cited authors are truly willfully ignorant of widespread American Indian influence on the intellectual development of the Enlightenment, I would say that at the very least, there would be a strong trend. That said, I think it is worthwhile to push back against some of the assumptions in Graeber's text itself.

Let me preface this by saying I rather like Graeber. I think that he posits some "big ideas" that are often very interesting to ponder. I am also sympathetic to his pronounced political beliefs. That being said, he is incredibly sloppy when it comes to actually doing history. This is because Graeber is not a historian, he is an anthropologist. Furthermore, he is not a historical anthropologist of Enlightenment France or any Native American culture.

After reading your question, my interest was piqued because your quotation makes no reference to specific "Enlightenment thinkers". Rather, it merely suggests that some of these writers expressed ideas taken from American Indians. So when I went to the library after work, I checked out a copy of the book, and I followed it up. They make no specific reference to specific writings of Enlightenment philosophers. Furthermore, the citations they reference for this purported influence all seem to be focused on the way American Indians may have influenced the structure of the American Constitution. If you follow Graeber's citation of himself:

In 1977, an historian of the Iroquois confederacy (himself a Native American and member of AIM, the American Indian Movement) wrote an essay proposing that certain elements of the US constitution—particularly its federal structure—were inspired in part by the League of Six Nations. He expanded on the argument in the 1980s with another historian, David Johansen (1982; Grinde and Johansen 1990), suggesting that, in a larger sense, what we now would consider America’s democratic spirit was partly inspired by the example of Native Americans.

Some of the specific evidence they assembled was quite compelling. The idea of forming some sort of federation of colonies was indeed proposed by an Onondaga ambassador named Canassatego, exhausted by having to negotiate with so many separate colonies during negotiations over the Lancaster Treaty in 1744. The image he used to demonstrate the strength of union, a bundle of six arrows, still appears on the Seal of the Union of the United States (the number later increased to thirteen). Ben Franklin, present at the event, took up the idea and promoted it widely through his printing house over the next decade, and, in 1754, his efforts came to fruition with a conference in Albany, New York—with representatives of the Six Nations in attendance—that drew up what came to be known as the Albany Plan of Union. The plan was ultimately rejected both by British authorities and colonial parliaments, but it was clearly an important first step.

Though the evidence as it is presented is intriguing, and there may very well have been some influence, I would also suggest that the Roman Republic loomed large in the framer's historical imaginary. In the end, I would suggest that American colonials should not be counted among the "major Enlightenment thinkers", and Graeber and these other writers seem to not be able to tie any political concepts among the Iroquois et al to specific Enlightenment thinkers.

I think decided to poke around the references to look up some of the citations you reference at the end of your question. I looked through Franks 2002 at length. I think Graeber greatly misrepresents this work. The work is focused on the difference between the French term sauvage and the English Savage and the way the two groups characterized the American Indians they encountered. Montaigne is the primary "major" Enlightenment author referenced in the study, and he discusses the dichotomy between the sauvage, a figure with many noble characteristics but does not live in a settled or civilized society, and the cannibal, who exhibit the basest characteristics of a society developing beyond the sight of european civilization. This is how Ritchie Robertson describes the Enlightenment's treatment of Native Americans in his history of the Enlightenment. These society exist almost as a theoretical model for the evolution of societies. If anything, Franks does a better job than Graeber of connecting American INdians to the Enlightenment, highlighting the way that French writings (though I would not call Missionary writings "enlightenment) praise the equality of Native American society and the freedom of their people, and the author makes a VERY BRIEF reference to the impending French Revolution.

TLDR, it's sometimes a good idea to follow the footnotes.