There isn't really a lot of official information regarding Veras Darkshadow the "rogue" member of the Illdari Council from Black Temple. However simple deduction does give us a bit of background and insight into this elusive character.
The Illdari Council is made up of four blood elf representatives from Kael'thas who have a dual purpose job. They are required to both watch Illidan, reporting back to Kael anything that may impact the blood elf interests and at the same time offer the Betrayer whatever support he may require in furthering their joint goals. The question arises as to whom their ultimate loyalty is with, Illidan, Kael'thas or someone else completely (such as their OWN personal interests).
Veras would have been one of the most talented Assassination rogues from the cream of the crop that Kael'thas took with him to Outland. However there is some speculation that in Veras we are also seeing a bit of the Demon hunter. Perhaps due to his close association with Illidan. The reason for this speculation is Veras' costume. He is actually sporting a recolored tier 6 Warlock skirt, the traditional demon hunter tattoos as well as a matching set of Fang of Vashj. The daggers give a hint that Veras was a part of the Blood elves migration to Outland since it was Kael'thas initial deal with Lady Vashj that brought them in contact with Illidan in the first place. Like all rogues however he suffers from a version of the "vanish bug" in that a few seconds before he reappears he is both visible AND attackable to those close to him, he can even be marked.
Some consider Veras to be the most dangerous member of the Illdari Council as a direct result of his rogue abilities. His Envenom can cause 9to10k damage in a matter of seconds, easily causing a player to expire before a healer can react to save them. Yet when he is not in stealth he is stunable and has VERY low armor. (Not surprising when you consider he is running around half naked to show off his manly chest.) Yet he is quite confident in his abilities to counter any comers as can be seen in his dying comments "You got lucky!"