I'll rephrase the question a little differently and mor common .
Must be someone who leads ceremonies or lives as a healer, having grown up in his culture?
If someone was adopted as a baby or critter by a white family and thus torn from his culture, could he can come back after years or decades on the reservation and then become a ceremonial leader or medicine man (I can not find a suitable word)? Is this possible or not?
Natives who can not grow up in their culture, are different formed / affected in their human being and this character "being Native" can not be easily learned or acquired. Is there a lack in the foundation of native way of life to learn about it?
Anyone can acquire knowledge, how a ceremony is conducted, how to perfom healings. The question is not just "how" and from "whom" the knowledge is acquired, the question is: Can a person who did not live on the res, develop a deeper and correctly understanding for this work? Or is this foundation missed?
The various opinions are determined controversial, the moderate opinions of one, the strict views of the hardliners. And it is surely different from the kind of ceremonie, the tribe etc.
I think this is a discussion by Natives ...