Diablo – Is healing blade nerfed too like all other life steal

Item perks like movement speed or life steal are individual and not shared with your party or follower. Class skills, on the other hand, can imbue party members and your follower.

You get 20% of your follower's added Magic Find, Gold Find, and XP bonuses.¹ You followers don't have drops and only add to your stats.

You get none of your follower's resource bonuses, and Strength, Dexterity, and Intelligence perks increase damage for the Templar, Scoundrel, and Enchantress, respectively.² +Vitality gear adds 10 follower HP for each point.

I think you have several choices to defeat Rakanoth:

1. Build up your Vitality or Armor so that your HP exceeds the damage he doles out with one teleport attack. Then - heal yourself via potion or Nether Tentacles.
2. Rely on luck: As a demon hunter, you should be boosting Dexterity, which means your dodge rate should be non-trivial. Also, if you keep him on the screen, he seems to be less likely to teleport attack you.
3. As far as builds go, Vault and Caltrops won't help against the teleport attack. Smoke Screen paired with the Tactical Advantage passive may be helpful to help you run away once struck. You'll want to maximize your DPS to keep the fight short as possible. The shorter the fight, the less time he will have to teleport attack you. Given that you're on Nightmare, I'd advise Impale + Chemical Burn.