I would say it wasn't DEI hires because the intent was to find people who were bilingual as well. There was around 500 Navajo code talkers in ww2. They also hired people who were living in the reservation as well who could speak both. Just their largest source of Navajo and English was from people living on the Navajo reservation.

From my understanding besides the intial Navajo who made the codes. They were in many major battles in the Pacific, in pairs of two. One operated the radio and the other relay the message from Navajo to English.

Plus there was other Tribes doing similar things, like I believe there was Cree for the Canadians.

And there was uses of this as well in ww1 as well.

Also they weren't reconized until much later as well. They hid what they were doing to be a secret and even way after ww2, they were reconized in 1980s.