This is, I think, how to get the Zorua:
I've checked in a lot of places and they all say to do that, so I'm pretty sure that is credible.
Zoroark is NOT a legendary Pokemon because of a few things that set it apart from other legendaries. From what I know, legendaries have at least two defining characteristics that zoroark does not share.
1) Legendaries can't evolve. Zorua evolves into Zoroark.
2) Legendaries either do not breed or do not breed normally. MOST legendaries are in the Undiscovered Egg Group, with the exception of Manaphy. However, Manaphy does not breed normally; you get a Pokemon not part of Manaphy's evolutionary chain when you breed it with a Ditto. Zoroark breeds just like any other non-legendary Pokemon.
I hope this helped. If I'm wrong on anything, please correct me!