I can confirm, after just recently watching events unfold, that NO, you can not kill a ‘scouting’ thrall outside of PvP window (the event happened on an official PvE (c) server). I saw an npc walking by my base (to which I thought to myself, that is indeed unusual) as my guards would have normally attacked it. I then noticed it had ‘scouting’ above it’s head and so I followed it for a while (trying to attack it a couple of times, but to no joy). It then came across the Brute in Unnamed City, which did attack it, and eventually killed it. I then went in and helped myself to his goodies, as well as finishing off the Brute.