Not sure what you are asking? Why would you need to contact FileMaker Inc.? Did you need to contact them the first time you installed?
You cannot run two copies of FileMaker Server on the same OR on different computers. So you have to uninstall on one before installing on another. But if you need to re-install FMS12 on the same computer, you can definitely do that. Usually you uninstall first.
I think we need more information to answer your question adequately.
If you are trying to set up a hot spare, you can, but with a couple of exceptions.
You can't have two servers running with the same license key at the same time. So to set the second server up you must shut down the first. Moving the license from one server to the next is a matter of shutting down the first and installing on the second. If the first is going to be used for other purposes then definitely uninstall. You don't want FMS starting up and both servers seeing each other.
The situation could occur if a server breaks down, gets stolen etc. If that's the case a new server must be up and running in a few minutes. Theres only one server running at a time. In earlier versions of FMSA you needed to contact FM in order to activate the FM-serversoftware on the new server. This is of great concern if this process takes to long. If you dont need to contact FM Inc to do this anymore then theres no problem. If it's still the case how long time do you have to expect to wait until you can activate the serversoftware on the new server?