Compare the "native" clothing worn in the ceremony with the native clothing of the same groups in museum collections, old photographs and drawings from pre-1900; then with similar materials from the 1900-1930 period, then with the way the Indians were dressed for the ceremony. The homogenation is evident.
This is not to say that some Indians do not strive to maintain tribal characteristics. Nor can it be said that there was no commerce among the tribes; there was a lot that has been documented for the pre-Columbian as well as later periods. Some groups had "rendezvous" like the one portrayed for the pioneers; I am only familiar with the San Fernando Festival held at Taos Pueblo on Sept. 30 (opened to others about 1880?). I have a collection of old photographs taken by photographers (my grandmother was one) between 1900-1905 of people at the Festival, at which members of various Plains tribes, from as far away as Montana, among others, attended. Beadwork and dress seen in these photos and others still has distinctive patterns (but, of course, the Pendleton blanket was already very popular among all the groups).