Giftcard Zen is just a middleman for selling the cards; they don't actually take possession of the cards and therefore, there is no way for Target or anybody else to know the card was even purchased from the public site. It is possible to ID a string of gift card numbers that were fraudulently purchased and later resold (like the recent Lowes data points), but that would be coincidental that they were sold on Giftcard Zen or any other site.
To illustrate this, if you have loaded any of the Target giftcards you've purchased from Raise, Giftcard Zen, or even Target itself, go into your account on Target and click "manage cards" not "manage gift cards" under the Wallet section. You will get a list of all of the gift cards you've saved and/or used to your Target account. If you click on any of those cards, it will bring up a history of it's use. Many are from Balckhawk (the card issuer for third party retailers) and Target.com (cards bought directly from their site), but most are from store credits from various Target stores across the country. These credits could be from legitimate returns or they could be from fraudulent purchases and refunds. It will list the city of the Target location as the starting balance and then whatever transactions have occurred on the card to date.
Again, there is no way for Target to know where you got the card from or what you've paid for it. One thing that would be possible for Target to do if they don't like reselling of giftcards generated from store credits is to program into their fraud detection or risk mitigation software the ability track if someone having a Target account with a physical address in lets say Atlanta is using a card that was last used/issued in lets say Portland. That in and of itself obviously doesn't indicate fraud, but a consistent pattern of that may make them unhappy and lead to a ban. Or they could just not allow the store credit giftcards to be used online like Lowes did.
