Can isolated neutrals, such as the Duergar Traveler, be attacked without DM supervision?

We'd prefer that you contact a DM when you initiate combat with any non-hostile NPC, since there may be a reason (plot) behind their presence. Plus, if the attack goes through, interesting things can happen. Sometimes we've stemmed minor plots out of random encounters such as that.

Just to clarify, -always- contact DMs before attack a non-hostile NPC, no exceptions.