I probably already know the answer to this one… but how viable are they in terms of survivability, CC and dmg?
Depends on the kind of build your running.
Witch Hunters in general are a bit squishy though (imo).
But it’s definitely HC viable. To be honest you could die on a Warder (the most tankiest combination imo) as well if you’re not careful enough. It all depends on your playstyle and build
For hardcore I would do the ranged witchhunter build with blade spirits, the 2 heals (obvious), Draeg’s (with or w/o transmute), Amarasta’s blade burst.
This setup is made around the Quillthrower of dreag crossbow.
I tried both a melee witchhunter and the ranged version and this one survives much better. The cool thing is you can assign the Tainted erruption skill (from the abomination devotion) to the blade spirits and they will work at their location instead of your own.
So I have not played it a good while since I lost all my items due to me forgetting backup before format c: (duh :rolleyes:)
Figure out yourself how it fares in 1.0.0.6 
If you get into melee, which I did, I stongly recommend maxing circle of Slaughter. With + 5 skills you have 60% fumble on it. You will hardly get hit unless it is AOE damage.
Survivability requires smart or rather not dumb play on your part and +hp items will help a lot as you will be low on health and DA. CC is not amazing, but not horrible. Curse slow is enough combined with high DEE+other poison damage as ranged. If you are melee then ring of steel/frost with at least a few points into the fumble will work wonders