People do use Regeneration Gear a lot in Faction Wars.
A lot of Factions don't have very good healers so the healing can help.
The only problem is Rugnor is a Dwarf.
Stage 21 Dwarf Faction is the Ignore Defense Boss.
You are going to want your Rugnor to heal, but you will also want him to have tons of Health.
You will need him with a lot of health to survive the hits of the Stage 21 Boss.
You might be better off with the Immortal Set vs. Regeneration Set.
The Immortal Set will give you Healing + extra Health.
I guess it all depends on whether or not you have a Reviver for the Dwarf Faction.
If you own Maulie or Steelgirdle, You could run Rugnar in Regeneration gear.
Than if Rugnar dies
You can resurrect him.