I think a lot of you guys are missing the point. Of course anyone who is paying close attention and is knowledgeable about mechanics and movesets is going to be able to tell a Zoroark most of the time. The purpose isn't to fool those types of people, the purpose is specifically to catch those who aren't paying close enough attention, or who don't know the full movepools of almost all pokemon. For those of you who play TF2, you'll know the way this works from the Spy class. Experienced players won't be fooled by almost any disguise unless you go to extreme lengths, but you'll fool many, many more who aren't so experienced or perceptive.
Still, this isn't going to win you any high ranking battles or tournaments obviously. It can help with laddering however, as a lot of the people you're playing aren't going to have their whole attention on the battle, or won't be experienced, etc.