I don’t know which Army code talkers of WWI were citizens or not, but Indians have been becoming citizens since 1831, so who knows about those individuals?
You don't have to be a citizen to serve in the US military. These days a Green Card qualifies you. In fact, Green Card holders are subject to the draft lottery, just like natural-borns.
We've had quite a few ferriners fighting on our side in every war. In the War for Southern Independence, a third of the yankee army were foreigners. An American family could buy their boy out of being drafted and they'd hire a European immigrant to take his place. That's how Joseph Pulitzer came to America, recruited back in Hungary to join a yankee cavalry unit, and his passage to America paid by his recruiter.
There were some famous ferriners in the Revolutionary War, too, some of whom were just looking for a good scrap and went back home to Europe looking for still another scrap when our war was over.
The WWII code-talkers were little-known until the Nicholas Cage movie, "Wind Talkers," but even fewer know we also used Indians for code-talkers in WWI.
As the "Front Lines" in France got swapped back and forth, whenever the Germans made forward progress they tapped into the Allied telephone lines, then ran a trunk line back to their switchboard. With all the mud and all the wire and wire repairs, it was easy to conceal their "tap" into the Allied communications. And there was no way to clean it all up without completely disrupting allied communications while the clean-up was under way.
All of the Allies' attempts at sneak attacks were failures because the Huns were listening in to all the te And they listened in on everything that was going on. lephone conversations. Until they started using Indians as telephone operators. Cherokee and Choctaw I remember, but I'm thinking there was at least one more tribe, too (can't find my notes on that right now). And the first major successful counteroffensive they managed to mount (the name of which escapes me) was credited to using Indian code talkers, which was the only way they could figure to maintain the element of surprise.