Can't you just target them with the bow though? That shows the Health Bar. Other then the zealots and quests the things are tied to the zone so you just have to watch that. I had one of the Reda quests on the border of a zone and 3 or 4 saves it was double in power. One save randomized their location in the lower zone and it was way easier to take them on.
I haven't run into it that much though since I usually don't stray across the zone borders. And I'm over leveled for the areas I am doing since I'm doing as much of a zone as I can before moving on and did the first seer quest zone.