I know I can access my Roon server with arc. But, will Roon allow me to have a second instance of my server software at a second location on a second network with the same, one license?
Not at the same time, you have to swap the license.
With one License, you can only have one instance of the server running at a time.
You can have multiple servers set-up and ready to use, but with only one license you will need to “deauthorize” the other server(s) and only authorize one server for use. This is easily done from the Roon app on the server you intend to use. There is no limit to how many times you can move the one license from one server to the next.
For more info see here"