Activist Suzan Harjo provided a list of talk-show appearances:
More on Oprah
Coincidentally, someone else asserted that Oprah Winfrey had never done a show on Native Americans. I said she visited the Navajo Nation (in 2006), where she got in trouble. For staging a non-Navajo powwow, I think.
And there was this: Quileute Chairwoman Visits Oprah. Add these to Harjo's examples and Oprah has done at least five shows on Natives.
Still, the Oprah Winfrey Show did 4,561 episodes in its 25-year history. Given their percentage of the population, Natives should've appeared in 50 or more episodes. Five or 10 suggest Natives were grossly underrepresented.
For more on the subject, see TV Shows Featuring Indians.