[link|http://www.aap.org/nach/Halliday%20presentation.pdf|Overview of the Indian Health Service]. It doesn't mention fluoride.
I don't doubt that health care, including dental care, among Native Americans is poor and substandard. It's a crime that they've been treated so badly by the USA for so long.
The closest article that I've been able to find that talks about fluoridation issues on Indian reservations is [link|http://adr.iadrjournals.org/cgi/reprint/11/2/210|this] 7 page .pdf. It compares Navajo and Lakota experiences with Baltimore and San Antonio. Unfortunately, it doesn't come to any clear conclusions (at least none that jump out at me quickly) but does discuss many factors that make comparisons difficult.
Cheers,
Scott.
(Who realizes that this should have been branched to Epi and Health quite a while ago...)