Well this what they say in the Rules Compendium:
Q. The wording on Darkness Energy from the EX:Ruby/Sapphire expansion says, "if the Pokemon Darkness Energy is attached to attacks, the attack does 10 more damage to the Active Pokemon." Does this mean that you get to add +10 even if an attack does no damage at all to the Defending Pokemon (i.e. EX:Sandstorm Murkrow's "Surprise" attack)?
A. No, it still applies only if there was initial damage to add to. So in other words, you still have to do some damage in order to have "10 more" done. (Sep 18, 2003 PUI Rules Team Meeting)
This should answer your question, well keep playing