As stated, you can get Necromantic Healing spell in Dimhollow Crypt. In the soul cairn there is summon boneman, summon wrathman, summon mistman and summon Avark. They work like any other summoning spell.
On the dawnguard side, you are sent on a quest to get 3 other companions and once they arrive at the castle they become venders and can purchase Sun Fire, apprentice restoration, which works like fireball. Stendarr's Aura, adept restoration, which works like guardian circle and Vampire's Bane, adept restoration which works like a cloak spell.
This.
I understand that many things are well hidden in this expansion, but that's Bethesda's little way of breaking a lot of people in to not having their hands held quite so much (this is all my opinion and assumption). With a little exploring, all of these secrets will be yours. Just take the time to slow down and look everywhere.
After all, as far as your character is concerned, time is very much on your side.
