The Gloom rune of the demon hunter's Shadow Power skill is as follows:
Is the 35% reduction in incoming damage in addition to the 15% damage done as Life, or instead of it?
I sometimes have difficulty determining this for other runes. For example, the witch doctor's Rabid Dogs rune indicates "Your Zombie Dogs gain an infectious bite..." and "Swallow your Soul" indicates "Gain X mana...". In these cases, the effect specifically indicates that it is in addition ("gain") to the base skill.
You are misunderstanding what "damage done as Life" means. When Shadow Power is active, 15% of the damage you deal to others is returned to you as life. Therefore, there is no overlap between the base effect and the rune effect; you gain life from damage dealt while also reducing the damage you receive from mobs.
In case this wasn't the misunderstanding, then yes you do get both effects. A rune effect only replaces the base effect if there is wording to that nature, for instance, the Companion rune effects all say "instead of a raven."
