Unfortunately, I have to stop using the bat, because he is very aggressive and attacks things even on the edge of the screen, including nasty champ packs whose affixes I'm trying to get a sneak peek of, and goblins. Can't unsummon him either.
So now I have no idea what to replace it with. Some possible choices are multishot suppressive fire to regain disc, caltrops with torturous ground (stuns when triggered), spike trap with scatter to damage fast leapers while kiting with evasive fire, or something that will allow me to deal with reflect damage mobs (60 dh died by nearly one-shotting himself on reflect damage rares in act 3) without using up disc.
One of my favorite defensive skills is Rain of Vengeance (Stampede). If you handle it right, it can help to keep nasty un-kiteable champ packs and minions away from you for a few seconds, block a doorway/corridor, etc. I also like Caltrops (Torturous Ground). I don't know what you would do about Reflect Damage mobs except to avoid them. Nether Tentacles kinda helps but you're already using Frost Arrow and "kinda helps" isn't always enough to keep Reflect Damage manageable.
Good luck! I don't have the brass to try a DH on hardcore.
You'll need a gear change to fight against reflect damage by stacking up on Life on Hit. My tip though is just to run from these guys, they are more of a pain and in HC you can't really afford that pain.
Caltrops Tort Ground is a new favourite of mine, I was sceptical at first but after reading the forums and actually trying it out it is a VERY good skill that will let you close some nice distance.
I personally hate Evasive Fire, but perhaps that is due to my inability to work out how to use it to it's full potential.
I've tried rain of vengeance stampede before. It's surprisingly useful, particularly because it has no cost, but it's very situational and has a longish cooldown. I'd rather have a skill that I can make more use of.
Torturous ground is indeed pretty good, but I'm weary of using anything that costs disc because of how essential smoke screen is.
Hmm, maybe marked for death with mortal enemy, to make the loss of the bat less of a problem.