Denis or Dennis - doesn't change the meaning - goes right back to ancient Greece and the god Dionysos; you can see that the name has become syncopated over the millennia. Dionysos was an oriental god who entered the Greek world rather dramatically and had to be fitted into their generous system. He was the god of wine, and of things connected with it, including the kind of prophetic inspiration that isn't reasoned or structured - it just comes welling up from the secret darkness. An alarming god, disruptive and subject to mood swings, but basically a benefactor.
Sorry to take brown warriors out of the meaning - that would have been wonderful for you - but the wild, shamanic links sound good to me.
How did Native Americans get their surnames? Given names I can understand - Native ones in translation, plus missionary names and then just mainstream ones - but perhaps there were names that sounded familiar to early speakers of English, who would have been the ones to write them down, and they would then just go on happening and the original name they'd been based on would be forgotten? I'm guessing, but this sounds possible.