Same problem here, Server is not showing on steam, the worst is that i started the server from the rfactor launcher in steam version.
I did the same tests that Depco did. I will let the server started for the next days, so you could see the problem...
https://world.rfactor.net/server-list - Uses the http port, search for the key "[RW]", you will see the server
http://servers.proracing.club/ - Uses the steam ports, search for the key "[RW]", you will NOT see the server
http://www.yougetsignal.com/tools/open-ports/ - Port Forwarding test: 64298 / 64299 - Port is "closed", because steam is not listening.
So, to confirm if my port fowarding is correct, i started a python http server on ports 64298 / 64299, and the port forwarding test has passed.
There's a obvious problem between rfactor2 dedicated and steam.