Well, for previously stated reasons, yes Salamence is a bad example. But it is a good point that zoroark doesn't have to be used before the pokemon it is pretending to be. Its just another mindgame he might be able to pull with this interesting ability. I do think this method will be less useful. If entry hazards are as common as they are now, particularly Stealth Rock, then such a move will be hard to fake, as it relies on the original pokemon not being hurt.It won't work with Salamence though because of Intimidate.
It will be interesting to see if his ability looks at the pokemon currently in the second slot, or the one in the second slot at the beginning of the battle. From what we've heard so far, I think it's the first, and that also makes the most sense to me.
And I hope they don't have any transformation animation when he switches in. That just ruins the whole point of the ability and just makes it useless.
I also hope that there is a certain amount of damage needed to break the Illusion, or that entry hazards don't break it. The damage from Stealth Rock could still give it away, but If you aren't using him as a lead, you'll probably want a spinner if neither of those are the case.