It's maybe not stated in the rules, but most likely if you'll get spotted, eBay won't be happy with it...
It's just how eBay works - they even regulate the size of banner you can use in listings to drive traffic to your eBay store.
However, with new rules eBay really shouldn't care much about whatever someone buys from a listing or a shop - as fees are the same (there's no more "Shop Format").