Does health regenerate in combat at all? I never see my health bar tick up during combat the way magicka and stamina do. Are passive and active skills that increase health regeneration worth taking/using at all?
Well first we have to set a difference between +percentages (for instance +15%) and flat percentages, or in ESO's case: flat numbers themselves.
Your calculation would be correct if not for the fact that it gives you +138% health regeneration. Not 138% health regeneration.
We have to determine where the +percentage is going to apply on; the base. Which would be the number that your Health Regeneration is stating in a neutral state when looking at your Character Menu (C).
So say you have 10 health regeneration in a neutral state, the +138% would then give you 23.8 health regeneration for 6 seconds in total. The numbers I'm using might not seem correct because the armor and racial passives are always up, even in a neutral state, so it's hard to know what your actual base value is. But we are also assuming that the 95% of Restoring Aura is added to the base of your health regeneration, not to the number with the added % of the racial&armor passives.
Now that the math is out of the way, let's get on with the practical part which is your actual question, I tend to digress from time to time.
You could use Restoring Aura as a replacement for an instant heal, in this case Rushed Ceremony . But as stated, Restoring Aura is NOT instant.
For instance: When your tank (or anyone for that matter) get's a huge burst of damage thrown on top of him and he can't get up to block, he'll take even more damage. You'll want to have an instant heal at the ready to give him time to get up and start tanking and health regenerating again.
General tip: It's never bad to switch your skills for different fights. It's understandable that you want to have the perfect skill-set but I believe it's not there. Every PvE or PvP situation asks for different combinations.
Restoring Aura gives +15% health regeneration passive, and +80% health regeneration active, so that is 95% from the skill, +28% from armor, +15% from racial, making it 138% health regeneration for six seconds. Would that allow Restoring Aura to replace an active direct healing ability such as Rushed Ceremony?
General tip: It's never bad to switch your skills for different fights. It's understandable that you want to have the perfect skill-set but I believe it's not there. Every PvE or PvP situation asks for different combinations.
Yeah, in a group you can do something where you have no offensive skills on your bar at all (Restoration staff, some buffs...), but you'd never do that in solo PvE, it wouldn't get you very far (you'd probably have 2-3 defensive skills and 2-3 offense).
For instance, my gameplan for dungeons has the following setup on one bar right now:
Healing Springs (Large AoE heal, morphed to return a chunk of the cost. Ideally tops off party mid-fight)
Rapid Regeneration (Two targets. Main purpose is that it's a powerful, efficient HoT on the tank and whoever is most damaged)
Combat Prayer (Area heal, smaller than Springs, but buffs everyone's offense and defense.)
Obsidian Shield (Not sure which morph would be ideal at this point, but it's preemptive "healing" on the whole party)
Molten Armaments (Buff party damage output)
This is bad solo, because I can't do enough damage with resto staff heavy attacks to down 1-2 enemies and get to where I can handle incoming damage with my healing before I die. (In ordinary groups of trash - it's fine on elites, who have less total damage than 3 regular grunts and with just one blocking, bashing work better). In a group situation, I can keep buffing the party and patching them up for a while (resto staff's magicka on heavy is essential to this).