I Googled around but didn't find much. For what it's worth:
http://www.lapahie.com/FAQ.cfm
A summary for visitors: The Navajo Nation (reservation land) is a separate government entity on a level of authority comparable to the US Federal government. Within the reservation territory (which covers an area larger than the 10 smallest states in the US and which includes parts of Arizona, New Mexico, Colorado, and Utah) the Navajo Tribal Code supersedes local, state and most federal laws. The Navajo Tribal Code follows a similar pattern to state and local laws in your home state, and common sense will easily keep visitors from running afoul of the law. But visitors should remember that they are visitors and should treat the land and people with the same respect that you would expect of visitors who come to your neighborhood. Possession and especially distribution of alcohol and drugs are prohibited everywhere on the reservation.
Firearms are prohibited. Fishing, hiking, and camping are permitted with a license which is available from the Tribal offices in Window Rock. Guided back country tours, horseback excursions, river rafting and such are available from operators licensed by the tribe and located near most of the major tourist attractions. The Navajo people mostly welcome and enjoy talking with visitors from other places, so long as they behave in a civilized and respectful manner. Photography of individual people or their dwellings is considered disrespectful unless permission has been obtained in advance.
Perhaps a call to the Navajo Nation Police would be in order? Would you please laet us know if you find a definitive answer to youe question?