Ahem. Active Zoroark user here.
I have no idea why bluemon suggested disguising it as Stoutland. Sure, this may work against inexperienced players, but against any experienced player, the strategy will fail. Not to mention, Stoutland and Zoroark both share a Fighting weakness anyway.
Really good disguises for Zoroark include Heracross and Mew. Mew is especially great because it can learn Nasty Plot as well (and someone using Nasty Plot Mew wouldn't look very suspicious either), so Zoroark can still use Nasty Plot while disguised as Mew and retain its disguise. Heracross will still be an issue, though, although only Scarf Heracross will be an issue (which is still bad because Scarf is Heracross's most common set IIRC). You will certainly need a teammate that can get past Heracross. Really though, you can use just about anything as long as SR, (Toxic) Spikes, and Sandstorm damage won't give it away, though I do recommend avoiding disguising it as another Pokemon that has a Fighting weakness. It won't go well.
Like Heracross, Cobalion can also cause problems for Zoroark, especially if it comes in on Dark Pulse/Night Daze. Typically what I do about this is use a Scarf Heracross of my own to force Cobalion out.
Also, through my use of Zoroark, I've noticed that using Dual Screens with it actually really helps. Don't count on this letting you survive Heracross's Close Combat, but neutral attacks that OHKO it otherwise will usually turn into 2HKOs. Xatu's a good teammate because it can set up these dual screens, reflect status, use U-turn, and even use Wish.
Either way, when it comes to disguising Zoroark as roflStoutland, don't do it. Just don't.