The
Cox AUP says:
Servers. You may not operate, or allow others to operate, servers of any type or any other device, equipment, and/or software providing server-like functionality in connection with the Service, unless expressly authorized by Cox.
But that's pretty much bullshit. Anything that opens a listening socket is technically a "server."
What kind of gaming server are you talking about? Like hosting a network game? That would definitely be fine.
There's really no way to tell if you're "running a server" or not if it's on an obscure port somewhere. As long as you're not running a massive anonymous ftp server or web server (which they block anyway) I'm sure you'll be fine.