I doubt Eminem had any involvement with the advert at all.
My guess is that Apple somehow used other Eminem footage along with animation of their own to promote Itunes hoping that Eminem wouldn't mind as it also serves as an Advert for curtain call. Some of ya'll may remember Em stating he would never endorse a product.
Though saying that, perhaps this is a new partnership also being used to encourage people to download using Itunes and not illegally .. decent video nonetheless.