A URL, or embedded content as part of HTML?
If it were just a URL, even an HTML-enabled client would show just the link. I assumed that it must be embedded content, which would be rendered as a normal-looking message.
Maybe it's both. But even so, I'd just see the link. And generally, I ignore blank messages containing links.
Also, it's not uncommon for email list software to strip HTML, and I doubt that it would decode the HTML before doing so.