Here are two recent posts on other sites about Native Americans in the First World War.
Soldiers Unknown is a historical novel by Chag Lowry which deals with the voluntary service of tribal members from Northern California. You can read about it here.
You can read here about Pvt. Thadius Sittingdown, Co. G, 2nd Bn., 358th Regt., 90th “Wild West” Div., who was a member of the Cherokee Nation.