It still wouldn't have hurt to have had some groups related to the natives. Maybe not natives themselves, but groups that adopted a lot of native culture. In Fallout: New Vegas, Zion park is full of tribes that are very similar to old native tribes. And Fallout has always had a big emphasis on tribes. Not necessarily native tribes, but groups of survivors that have, over the years, reverted to a very tribal way of life. Yakima being in an Indian reservation would make the likelihood of that even greater, yet no one jumped on the chance.