I don't have any experience with that site, however for that price I'd assume they are replicas. Infiniti I'd imagine has a fixed price on it's parts (including wheels), which is why factory things are all pretty much the same price no matter where you go. Price for those wheels at the dealer I'd imagine is over $600/ea.
Overall, replicas aren't necessarily bad, depending on who makes them. A lot of times, these sites that sell "OEM" wheels are selling replica wheels that were manufactured according to "OEM" specs, so they are exact duplicates, which is typically why they look exactly like OEM wheels but you can get them for much cheaper.
I've personally owned OEM replicas before (although not from this particular website) and I liked them with no complaints, they were solid wheels that looked exactly like OEM, but were about 50% of the price of true factory OEM from the dealer.