Just an FYI - Joseph Marshall III is more than just an author. He was born and raised on the Rosebud Reservation. He speaks fluent Lakota, has assissted in several language programs, taught high school and worked to bring traditional skills and knowledge to the younger kids there, was one of the community members that banded together to start the Sinte Gleska Tribal College, was one of the Charter Board members of the college, was part of the group that worked to re-introduce the wolves into Yellowstone Park, and he and his wife connie continue to work for youth and community self-empowerment programs ... and still writes books.
I have never heard anyone at Rosebud speak badly of him. If he has an excess of groupies it is probably because he never speaks badly of anyone and from what people in his community say, has an unfortunate tendency to not judge people or turn them away. Something that does bring trouble to his door.
I did not go through the book links on that site to see what was said or by who, but just from looking at the names - most are respected Native books.