I never disputed that. Power is always a temptation. That's why Draenei are so vigilant and act on the first sights of corruption.levixus has already proven that draenei can second guess their allegiances and seek demonic magic
Personally I don't even have a problem with playable Eredar. (My Draenei would have)
But Draenei Warlocks make no sense at all.
Actually Warlocks in general don't make sense. The guards of Darnassus or Stormwind would kill you on the spot if you'd stroll around with your demon out.
Again: One random rare NPC that has warlock abilities but no lore background whatsoever doesn't prove a thing.jurim's existence has proven that draenei can be warlocks without mutating into broken or man'ari.
I bet that the transformation to a man'ari is not instant. Such things take time. So maybe your NPC just has crossed over to the dark side (for the cookies, obviously)and has yet to mutate.