Why hello! As someone who has a character that was raised in that path and followed that trade for many years before taking up the lance, I can safely and sadly see this thread has about most of the lore on it. And you've taken the same idea with Raine that do with Tris: "This is what/how he learned, not how the Ala Mhigan shamans are." It works given his mother was an outcast and broadly considered a "witch" by the locals of the time.
To Teadrinker's point, I followed some of the same logic. Anything healing is really more an herblism/wortcraft kind of thing. I actually look at the alchemy recipes and wing it by dumbing them down with the basic ingredients, then adding the RP flair of smelling like a goats ass.
For magic, during the few and rare times you will see Tris put it to use instead of the lance? Look to 1.0 Conjuration spells. They are more fitting to the idea both highlanders and the Ala Mhigans being a rough and tumble sort of people. Note that the spells are almost entirely offensive.
Still, I'm being careful with this. While it satisfies the druid/ranger/pathfinder archetype I was wanting with Tris, I am fully prepared for lore to roundhouse his face as well. It's a sparsely mentioned element of Ala Mhigan life, notably in the Cactuar Piss quest. So I have to take a balancing act with it, and use some of my storytelling dynamics for the character to be not so upfront about being a shaman.
I would love more lore on it, and maybe Stormblood might toss of a few bones on that.
(if you see what I did there you get a cookie)