IMO, Volcarona has no "added-value" when combining with Houndoom EX.
First of all, Volcarona's Solar Rebirth attack can search and get a 'Doom, bench it and attach up to 2 Basic energy onto it.. Since Volcarona is a Stage 1 Poké, a requisite turn must be devoted first to get its Basic into play. So, 1 turn is lost just to get Larvesta(s) into play.
As an alternative, one could just use either 1) Hoopa EX, 2) Pokémon Fan Club, 3) Ultra Balls, or Bridgette to possibly and directly get multiple 'Dooms into play without losing any turn(s). Further, either a manual energy attachment or playing Blacksmith for multiple R energy attachment can place Houndoom into attack mode turn 1. No "speed" is lost by just using Houndooms.
Lastly, should one need a non-EX attacker, Volcarono only inflicts a meager 60 damage for CR energy cost AND you need to also discard an attached energy. On the other hand, Pokémon like AT Entei (AnO 15) is a far better choice, IMO, since its Ancient Trait allows it to attack twice per turn and the damage output is superior.
