Quick question.

Does the elemental protection perk in the block tree work against all types of magic or only against frost, fire and shock like the description says?

In particular, would it work against the vampire drain health spell?

Vampiric Drain and Drain Vitality (used by revered, legendary dragons and ofcourse, the Dragonborn) are magic damage, not elemental. Block tree's Elemental Protection will work only against fire, frost & shock.