Wowpedia says undead hunter's followed Sylvanas in her necromantic footsteps and have a picture of a undead hunter letting off a dark purple shot which is similar In color to the ones dark rangers show.
The pictures are also just taken from the Darkranger page you can see they use Purple shots/have a purple Aura and even Sylvanas uses a purple shot in the video I linked. No where in any of the dark ranger stuff is there black magic with Green.
Also were just gonna ignore that you were wrong about the deathknight Training ground/boot camp then?