Yes, it can be.
If you bring an event shiny Suicune, Entei, or Raikou to Lostlorn Forest via the Relocator, you will encounter a female Zoroark. You can catch it with any of the Poke Balls in Gen V (Poke, Great, Ultra, Master, Dive, Net, Dusk, Nest, Quick). So it CAN be legit if it's not caught in a Cherish/Poke Ball, as long as it has YOUR OT and ID. (Unless you got it in GTS)
Also, if you breed, it will ALWAYS be in a Poke ball.