I'm pretty sure that all third party sites are just using the same method as the launcher to check for server statuses, which is to query the following URLs:

http://frontier.ffxiv.com/worldStatus/gate_status.json?
http://frontier.ffxiv.com/worldStatu...t_status.json?

Third party sites are possibly caching the data for a brief time and maybe they're also additionally doing a ping to check for a response, but I don't think it's anything more complex than that.

That information is straight from Square Enix if the servers are up or not so I don't see there's really anything more you can ask for? We don't need to know how their data centre is wired up and they've provided us with an interface to query server status (which they deem as good enough since that's what they use in the launcher)