For what it's worth, I emailed American about selling these coupons and this is the response:

"We do attempt to discourage the auctioning of the Kellogg certificates, as we have specific agreements with certain
companies to distribute miles and are obligated to allow only those companies to distribute miles. But realistically, there
is little that we can do at this point to prevent individuals from selling or buying them on eBay. The AAdvantage department
does monitor the online auctions on eBay and may send you an email asking you to remove the auction.

Hope this answers your question."

Pretty much a "non answer" in my opinion.