Does Immunity to a type of damage or Resistance to a type of damage count as Damage Reduction?
Damage Reduction is a specific thing with its own specific rules. It never (unless you are playing with the change in Complete Psionic as opposed to the PHB) applies to damage from spells (even non-energy damage) nor energy damage (even from non-spells), for example, whereas Immunity and Resistance apply even to magical threats. So, while e.g. Energy Resistance does reduce incoming damage of a particular type or from a particular source, it is not Damage Reduction.