VMRC's control plane connection uses HTTPS over port 443 by default, but it can be any port number--vSphere may use 9443. The data plane connection uses a custom protocol over port 902 by default, but again, the server can configure any port number.
Internal ticket 1983585 is tracking connecting through vRA with a proxy, but this may not affect you.
Can you make a proxied connection using VMRC 9.0? What's your host OS?