These guys are good kills for raising faction with the Necro guild and the DE Queen in Neriak.
I don't know about the "Incantor" but the "Elementalist" and the "Shapeshifter" will both use a pet in combat. Since they often come to each others aid (and definately will if your HP drops too low) this means you will not face just one caster mob. At a minimum you're looking at 2 mobs, 1 caster type and 1 melee type. Double that if they gang up on you.
I strongly advise that you take them in a group at the lower levels (5-12). You will definately kill them easier and you'll gain the XP bonus along with the faction increase.