Found this on the Siebel Bookshelf:
http://download.oracle.com/docs/cd/B40099_02/books/Secur/Secur_PhysDeploy3.html
Siebel Business Applications do not support the translation of port numbers or protocol switching. An example of protocol switching is changing from HTTP to HTTPS. If you deploy SSL between the client and the reverse proxy server, then you must deploy SSL between the reverse proxy server and the Web server on which the Siebel Web Server Extension (SWSE) is installed. Similarly, if you deploy SSL between the reverse proxy server and the Web server, then you must deploy it between the client and the reverse proxy server.
Port Translation breaks Siebel App.