If Zoroark uses "Foul Play" to copy Blastoise's "Hydro Launcher" attack, do I have to be able to return 2 Water Energies to my hand in order to do the 100 damage?
No, the attack does not say "in order to" so you do as much of the attack text as you can.
Source: PUI Rules Team (2011-06-09)

Relevant cards

Note: All applicable cards may not be listed below.
BW1_71
HGSS2_13