The Dalish philosophies are interesting and I'm very curious to how they'll be portrayed and I am looking forward to both learn more about them and most importantly learn how different Dalish individuals interpret them differently.
Sadly, I don't think the PC will be the primary lense through which it's explored. NPCs will handle that. We will likely only at best be able to express agreement or disagreement to any one policy, with only slightly more context than a non-dalish (remember that this conversation will be neccessity be available to all pcs).
As for how a Dalish pc might be able to follow the Vir'Atishan... it depends... does it require absolute pacifism?
Ah, yes, the main problem with the dialogue system in DA. We, the players, can have lengthy discussions about this matters for years, but in-game our characters can only say a couple of lines. Although one could say our characters will talk through their actions.
As for the Vir Atish'an, little can be said for now, since the only thing we know about it comes from a pair of gloves (a bit depressing, if you think about it). From a gameplay point of view, it seems to point to a Dalish Mage Inquisitor, probably a healer. Paradoxically, an orthodox Dalish mage wouldn't choose the Spirit Healer specialization because they're afraid of spirit magic. As for roleplay, I doubt it would be a pacifist run, but a paragon run.
"Guys, guys, don't fight. The world is ending, you know. Why not stop this petty fight, save the world and then we can discuss this matter in a civilized way? I can bring something for a meal, my clan makes this amazing cold meat that..."
"Kill the stupid knife-ear so we can go on killing each other for no sensible reason!"
"..."
(Several minutes of screams later)
"You guys are very lucky I'm a master in the healing arts. Those nasty bruises, broken bones and bleeding wounds could have killed you if not properly treated".
"But you did this to us!"
"Sorry, were you saying anything? I couldn't hear you well"
"Nothing, nothing, Your Eminence!"
"Good. As I was saying, there's this delicious meat that..."