If the spell, attack or ability says no saves of any kind allowed, flaming or no regeneration saves then you are not allowed to make one! A regeneration save is no ward save or armour save.. So even a sword which says ignore armour and ward saves don't ignore regeneration saves! The fluff about regeneration saves is that regeneration restores any wounds that are made! So a troll got hit by a sword and the wound made isn't deep enough so the troll restores the wound!