Both are Native-owned, but I don't know anything about additives and their websites don't seem to have any details:
I've never tried either, though. Signal Tobacco has a decent selection but King Mountain is just cigarettes. Maybe someone else knows about the additives situation.
If you want just pure cured leaves, one non-Native tobacco business I do patronize is Whole Leaf Tobacco. Their stuff is about as unprocessed as you can get. They're also the only place I've found online that actual carries traditionally made & sourced perique. The only downside may be that they sell in kinda large quantities (I think my smallest order was 4 oz).