Grey Owl may not have been raised a Native American, but he adopted the lifestyle, beliefs and outlooks of those people. He turned his life around, made peace with nature and himself. I should imagine the Native American People would have been proud to have him as one of their own....and indeed if you look in this clip you'll see that they took him in as exactly that.
You can choose to see him as a drunk, a bigamist and a liar.
OR...you can see him as a very human man, with many faults, who faced his demons and conquered them. And then became a man who went on to do as much as he could for the planet, whilst also trying to make amends for his former life.