Mostly by theme and having it fall under the disciple of war rather then magic. Using MP doesn't disqualify on it's own for being 'non-magical' as some classes like the Bard uses magic for a portion of it's mechanics even though it still falls under disciple of war.
Depends on how you do it sure. Chloromancers from Rift, the example I knew and refer to the most, still had direct heals. Just the bulk of their healing was through doing damage. So if you gave something like only a direct heal and a party wide aoe HoT with the rest being damage orientated healing, I feel it might just work out fine.
