Even if you are wielding a weapon that deals the correct elemental damage, the effect will not trigger if you are under the effects of skills that change the damage type away from that element. Likewise if your weapon does not deal the correct elemental damage, you can use one of the skills that changes the damage type to that element to achieve the desired affect.
As for PvP, just about no good Dervish build uses Avatars. They all use [[Wounding Strike].
Avatar of Melandru or Dwayna is probably best for pvp. Lyssa is alright, but more of a gimmick. Grenth is pretty meh, and balthazars is just retarded. Condition or hex control on urself is basically all those 2 are worth it for.
Also, about ur 1st question. some of the avatars, as well as many derv enchants change ur damage type... check that out.
Also conjure is in the same packet of damage as ur scythe, so if ur hitting generally for more with conjure up, then its working. If not then check out effects in the area/on you.
Aura of Holy Might has an unwritten conversion to holy damage.