A combo of the stamped ET (offset) nnumber and no VW part number cast in says "aftermarket" to me.
Have you ever seen a modern OEM Porsche wheel without a part number? I never have.I have seen that top symbol on VW rims before. That coupled with the fact that a Porsche center cap fits. Tells me that it is most likely a Porsche wheel as they have there own specific center cap bore. Since you have Porsche center caps it is most likely not a reproduction because they usually sell them with a generic center cap due to copy right. Not to mention Porsche charges an exorbitant price for their center caps. So i doubt someone would go out of their way to buy Porsche center caps to go on a Touareg.