Yes, there was actually a deck a while back in the 2011 format (after the mid-season rotation) that was Yanmega Prime/Kingdra Prime/Jirachi. The Jirachi had an attack where you flipped 3 coins, and for each heads devolved one of your opponent's pokemon. Yanmega had a Poke Body that let it attack for 0 energy if you and your opponent had the same amount of cards in your hands, and Kingdra's spray splash poke power helped further spread damage.
But to answer your question, yes, that does count as a KO.