Does the OL Dodge card only last for the roll it is used on? I assume it is, but the part of the rulebook where it states that the OL dodge is like the Hero dodge left some doubt. Thanks for any help clarifying this issue.

The overlord's dodge card is played after an attack roll (including any extra dice the hero wants to add with fatigue) and forces the attacker to reroll any number of the dice that you choose (or cancels with an aim, preventing either side from re-rolling). It only affects one attack, but its effect on that one attack is the same as a hero's dodge order.