Well, routing games through a specific gateway can be difficult as the server addresses may change at any time. As mentioned above you can't route by a domain like "ubnt.com".
Actually you can add a route to a domain in linux, but this domain is resolved only once on creation. That means you add a route to "ubnt.com" today, it gets resolved to the current public IP and added as route (with destination IP, not the domain). As soon as the domain refers to another public IP (e.g. provider change or dynamic public IP), the route runs dry because it doesn't update the resolved IP.