Random spawn anywhere along the icy catwalks. These can drop any piece of Crystal Chitin armor, however such drops off crystalline hunters are ultra-rare.
Ive gotten tons of gems for the quested armors so far just farming Velks, usually the Tops shelp is where I see the hunter the most. Although Ive seen him a few times, mostly I get the gems, and velium although I did get a pair of the Crystal chitin boots so far. Now that I know they can drop several other pieces Im going after them too. I used to just pull the PH spots from the deadly to the Frenzied but I guess I'll have to kill them all along that shelf now again, oh well, more velium for me to sell. I make about 1k a night if I can fill up 2 10 slot bags and still keep the gems, weps, armor, and small pieces. hope some of this helps others.
Procs a hard to resist cold based DoT called Deadly Velium Poison which cannot be cured by any spells and does 30hp/tick damage for 2 minutes(600HP total). It has been mentioned that the AA ability Radiant Cure 1 will remove this DoT but I cannot confirm that.
Uncertain whether these are also rogue type mobs similar to the Watcher/Devourer's.