If I start a region in one server, say US West 1, can I get to it in US West 2?
No. It is easy to check, and I just did. As North American servers are full right now, I’ve tried to log in to European server. I had no problem connecting, but once there I could only join games on that server, and start a brand new map.
That said, for the situations like this it could be beneficial to start that new game on the server on another continent so that you can still play something while your regular server is busy.