The energy is gained even if critical hit is denied by an effect such as Stoneflesh Aura.
Energy gain[]
This table will show you the total amount of Energy you will regain per use of the skill. Remember that since it's a Dual attack, you will critical twice unless one or both attacks miss or get blocked. Using zealous daggers or the Critical Eye skill will increase your net energy gain by two; using both will increase it by four, for a max net gain of 11 energy at 13+ Critical Strikes.