I have run a few quests solo with hirelings. A few things I was able to observe:
1: Hirelings can be targets of the hunt.
proof: was running retrieve the stolen goods and had a hound but no blue arrows so I thought I missed it. 3-4 minutes later had a second hound and I was the target. fairly sure at that point I didn't miss it. Hirelings can be targets.
2: Not sure what they are yet but at character level 4 elite quest level 2 hounds have around 200 HP. this is based on my max empowered searing light hitting for roughly 150-180 hp and taking the hound bar down to roughly 20% left.
3: Having a caster who can do a ton of spike damage is helpful. You can target them when the first spawn in and get a solid hit in before they even move or attack. that is how I have killed 4 of then with my little hireling group. When the hound only has 20 percent health left when it can finally act it is a lot easier to kill.
Hope this helps keep you alive.