Per GURPS Powers, using Control to provide DR requires a special "stunt" known as a Power Block. But to me it seems logical to make it a normal use of Control. If each level of Control can give you +1 to resist an Affliction, +1 to ignore a combat penalty, or -1 on an opponent's combat penalty (depending on the substance or energy being controlled), adding +1 DR doesn't seem very far-fetched or overpowered. And, with this rule in place, it then makes sense to allow a Power Block roll (instead of the normal IQ roll) to try to double the defensive effects of this ability.