I get no such error connecting there at port 6667. The fact that you're getting "connection refused" means the problem is not that /dns servername not finding anything.

I do get a different error message about an SSL certificate error when trying to connect to port +6697 because their certificate contains master.spiderchat.org instead of the actual round-robin address people connect to, so mirc thinks that a bait-and-switch is going on.

For the SSL issue, you can set mIRC to 'display invalid certificate', and you can selectively authorize mIRC to accept that certificate in the future. However that can be a problem waiting to happen, because whenever a future date happens that they add a new server to the round-robin address using a different certificate, or else their certificate expires or is replaced, then instead of auto-reconnecting while you're away from the keyboard you'll find yourself with the popup approval window again.