Hello
Can you please clarify if you want to use SAP Webdispatcher as reverse proxy or load balancer? I believe that you want to hide your portal URL behind sap webdispatcher exposing only the url of sap webdispatcher to the internet users. Please confirm.
You may refer sap help link:
Architecture and Functions of the SAP Web Dispatcher - SAP Web Dispatcher - SAP Library
Cheers,
Tapan