Good for them, but they have a snowball's chance. Because the offenders are not using the entire name: "Caddo Nation" and so it will be a futile fight. The same way you can say "Sacramento oranges" but you can't say "City of Sacramento Oranges."
It all depends on two factors: 1. How the Caddo Nation is 'recognized' (don't you just hate that term - that our existence hinges on the occupying government's 'recognition' of us?) and 2. if, and then how, they are incorporated. They have legal right to protect their corporate name, not (merely) one word of it. It has to be an EXACT and TOTAL infringement. They could file for a trademark and (another snowball's chance - but maybe the trademark clerk would be off his game that day) and AFTER they got a legal trademark approved, THEN they could start lopping off the list of offenders. But last time I checked trademark law (last year) I am pretty sure they would not be able to meet all the requirements. That should NOT keep them from trying though.