Yes, all Pokey's have them, but they all have different values. If one of your pokeys have an IV value of 0, then you cna go to mirage island. If you want to know if you're pokemon is an Mirage Pokey, either go to Pacidolog town and talk to the old guy who sees things (forgot which house he's in) and if he says he sees something then you ahve a pokemon in your party that has an IV of 0. Or you could just go to where the island should be and if it's there, you ahvre onve.
I think...