we have to wait for the English version for an official answer but when you activate an ability you do as much as you can, so if the translation is correct yes you could put him on the bench from the discard even if there is no dark energy in the discard.
Ho-Oh EX Rebirth ability is very similar to Darkrai's and this compendium entry is the closest official answer you'll get tell the card releases.
Q. If I flip heads for Ho-Oh EX's "Rebirth" Ability, if I only have one Fire and two Lightning energy cards in the discard pile, can I take all three of those?
A. No, you can only take one of each different type of energy, up to three total. So in this case you could only take one Fire and one Lightning. (Dragons Exalted FAQ; Aug 23, 2012 TPCi Rules Team)