The system would be useable. You just wouldn't be able to validate the certificate. That said, it's a fine line and I would consider the system down in this case anyway.
Right, but if their uptime monitor is internal, and they are resolving from an internal address, nothing is wrong.
There is the problem.
Yeah, but if your status page is made to be seen by external people, the right thing to do would be to monitor it just like if you were using it externally. There are whole slew of problems that wouldn't be exposed correctly if your monitoring point is internal -- like this exact problem, DNS, etc.
RIght, but since their customers are not internal, having a monitor that is not outside of their network would make for a pretty poor uptime monitor.