Palladium, for some reason that I think is not too hard to understand, seems to think that shamanism is an American phenomenon that is confined to the First Nations of that hemisphere. Furthermore, this seems to be confined to North American First Nations (due to Central America being overrun by vampires and South America being overrun with alien invaders of other sorts), so when one picks up RIFTS: Spirit West it is not surprising to see that the various Shaman Occupations are built on the assumptions that those Shaman are going to be First Nations (specifically, from the various Great Plains and Southwest nations or remnants originally from elsewhere that nonetheless relocated there). There is no concept extant that Shaman can arise in any other context, so there is no consideration given to any other variation thereof; this greatly limits the scope and scale of the Shaman Occupations in this book. Spirit West, therefore, is far more about making the mysticism of the 19th century Old West playable in a monster, mutants, and massive machines milieu than anything else.
That said, let's take a look at what's on offer.
The book has two Occupations that are not magic-users; these are two of the Warrior Occupations (Tribal and Mystic, respectively; the former is purely mundane, the second is a psychic.). The rest, be they labelled as Warrior or Shaman, are shaman variations; the variations are in emphasis and specialization, but otherwise they conform to the Shaman archetype of an individual chosen by the spirits to become a bridge of some sort between the ordinary and supernatural world. Totem and Spirit Warriors are Magic Knights; they trade some portion of mundane existence for a magical augmentation to their martial capacities, at the cost of some degree of behavior restriction (and an ongoing relationship with the source of their powers, which needs to be kept happy). The Shaman are, for our purposes, primary magic-users; they make the same sort of bargain, but are more about using their powers to aide the tribe and afflict hostiles using those powers themselves instead of in additional martial arts. These split by focus or source of their powers (Animal, Plant, Fetish/Mask, Elemental, Paradox, Healing), but otherwise are similar enough that one can generally grok one another's abilities and restrictions.
Okay, now, to extrapolate without resorting to outright mechanical revisions.
They chose you. Shaman are chosen, neither born nor made; senior shaman can, and do, foster their juniors (and societies of shaman chosen by a given spirit or spirits are very much a thing; priesthoods form out of them, should the circumstances allow it) but this is not necessary. The spirits are more than capable of teaching their chosen shaman how to do what they wish from him on their own; more formal priesthoods lack this they-call-you provision, which is a clear mark of distinction between these traditions.
Your powers are gifts from them, that come at a very palpable price. You are not an ordinary man anymore; you are taken up and adopted into the spirit world, to a certain extent, and you are expected to abide by the conditions that come with those powers, period. Your spirit patron comes first, always, and your duty to your people is--in large part--to keep them in harmony with the spirit world as your patron shows it to you. This can, and will, lead to conflicts between shaman societies when their spirit patrons' interests conflict. (Deer societies and Wolf societies are not friends.) A hippy you are NOT.
Your people expect you to represent them to the spirits. Bridges are two-way affairs, and the spirits expect you to be the one who relays between ordinary and supernatural. When the people are in distress, and are unable to handle things as they usually do, they will expect you to contact your spirit patrons and consult with them about the matter as best you (and they) can.
Now, that in mind, you're going to play a character that's not a self-serving loner. You're part of a community, part of a culture, and being a Shaman (any sort) means that you're participating in that situation--in that environment--and therefore you are part of both that tribal society as well as your shaman society. Keep that in mind when you chuck those dice and see that you can opt to play some form of Shaman; you're not a free agent, so if you don't want to deal in that sort of relationship work then I suggest you choose another Occupation.