Reading this post, it's clear you have no idea how Illusion works, or how Dragon Tail works.
Dragon Tail and all forced switching effects have no predetermined order in which to bring opposing Pokemon in; it's random. The order you put your team in makes absolutely no difference.
The minisprites don't update after Team Preview or when you switch things in or out, so the idea that Zoroark is "revealed" at any point just because the minisprites are on display is ridiculous. The Pokemon that is actually in your final team slot is only known to you.
Last time I checked, Dragon Tail sent the pokemon in a fixed order. And in the simulator it always sent them in the same order like that every time I fought a Garchomp with Dragon Tail. One would think after 100+ battles seeing Empoleon come in right away and Clefable afterwards it would be enough proof, but seems I was wrong after doing a second test. I find it particularly weird as the spanish translation on BW specified that it sent pokemon in order, I suppose it got changed. My bad I guess. I will do a retest on the cartrige once my 3DS gets fixed for a definitive confirmation.
Second, on Zoroark, I meant to ask for an old glitch that by the time you mentioned got patched long before, but didn't get fixed completely.
Before the patch, the sprites shuffled around and put the sent pokemon first, and Zoroark's minisprite changed to match the imposted pokemon, making trivial to track Zoroark as the sprite change was pretty visible, and even if it was the first time Zoroark came, all you had to do was look if the last pokemon had been revealed, as you would see TWO IDENTICAL SPRITES, immediately blowing away Zoroark's cover.
Sadly it didn't get fully away came with consequences: look at what happens on turn 2:
http://replay.pokemonshowdown.com/gen7ou-643320534
The sprites still get screwed. Fortunately, they no longer move and properly hide the status and HP%, and it even makes the (active) detal show up on the imposted pokemon instead of Zoroark. This visual glitch is just that, it no longer helps nor screws the Zoroark user. But still it would be nice to get it away for good. It's like the Transform not spoiling the ability error. A tiny thing, not in anybody's priority list, but that should be dealt with if possible.