Yes, the Pro/MMO project depends on the backend. The project is an example of how you can use the backend.
The project is open source, however. So if you want to do something else with it, please do.
Yes. Someone has to pay for dedicated server up-time. When I speak about this, I say “with proper configuration the backend is free for developers to use”. Proper configuration means that the game is collecting enough revenue from the players to cover the dedicated server uptime.