I find it VERY strange that out West that Native Americans are treated "racially different". Here in the South and when I lived up North, Indian Heritage is something to be "proud" about. I am VERY proud that I am 1/8 Indian. We have lot's of Indian culture celebrations in the area. Near my parents there is one museum dedicated to finding ancestors and displaying the history of the Cherokee Indians.
However, we don't have many Indian Reservations. The one's we do have is just for the gambling and casino's. They are not for the true heritage or pride of the Native American. That is truly sad.
The tow truck or other services not coming onto the Indian Reservation may not be racially motivated. It may be legal. Indian reservations fall under different rules. They are FEDERALLY controlled and NOT State ruled. That may carry some liabilities to business owner's when dealing with going onto Reservation land. Some business protections may not apply on Federally controlled property. I know if I don't feel my liabilty insurance on my vehicle would be valid in an area if I am to have an accident, I may not go to that area. For Example, In Mexico, it is illegal to have a car accident. Everyone leaves the scene of an accident down there.
So check out the local laws pertaining to the Reservation. Maybe there are truly some liability issues in the works that goes beyond normal common sense! Otherwise, sue the whiteman for trespassing on your property!!!