Diablo – Are Demon Hunter pets valid targets

As a fellow DH player, I've used the Templar myself.

I'm now on playthrough at nightmare mode - and I still feel that he's the one contributing most to my playstyle.

I can't say I've experienced any situations where I'd rather have one of the other companions.

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.