It seems to me that every non-Garlean combatant utilizes aether on some level (even if they're not consciously trying to). As for the player character job classes (machinist excluded?), I think it's likely that most supernatural feats activate the user's aether in some way. I don't care how angry a warrior gets, I doubt they're able to survive some of the stuff Holmgang lets them walk away from without some form of magic.