The famous Navajo Codetalkers were mostly in the Marine Corps in the Pacific. The Army in Europe had Comanches, Apaches, and Osages, among others, many drawn from the National Guard divisions from the Southwestern states.
I think you're right.
"I was under the impression that they were mostly Navajos"
You are correct. The History/Discovery? Channel did an excellent piece on these guys with all due honors to their efforts. Not sure when it was filmed but, as I recall there were about 6-8 guys still alive.
For all the PC BS that exist today, these guys were proud to serve and afterall one pointed out, it's our country too!
Given today's political climate the NYTimes would probably headline how Rumsfield seeks to exploit the helpless indigeous Native Americans.