It is the player's own responsibility to keep their IP private hard to obtain.
As far as the server goes, it shouldn't be too hard to keep it secret. Have everyone get a private profile/go offline on Steam for the match so that a hacker can't get the server IP through Steam, and only give the IP to trusted people.
Can't DDOS without an IP
http://play.esea.net/index.php?s=forums&d=topic&id=627837