Can I setup a Tor exit node using Virtual Private Server that uses VPN that allows port forwarding. Is that possible?
Answer to your question: you can join an exit node to the TOR network even if you are behind VPN. Therefore, I think you can set a VPN connection to the VPN server in the exit relay computer.
Maybe it is not the direct answer but you can connect to the VPN server using TOR. Check out my solution: