If I have a server, secured with ssl, which is setup as a reverse proxy to another server, will the traffic still be encrypted?
Simple. The traffic between the visitor and the reverse proxy will be encrypted, assuming the server is properly set up. The traffic between the reverse proxy server and the unencrypted server will of course not be encrypted. So you probably won't want this traffic to go over the Internet.
I sometimes use SSL-encrypted reverse proxies to give outside access to webmail servers inside an intranet. So the traffic between proxy and webmail server stays within the local network. A VPN between the two servers would also be a good solution.