From my experience, each application server requires unique ports. If you define multiple application servers to the same ports in the WebSphere Admin Console, you will run into a conflict upon starting the second JVM that prevents it from starting.
Is the question geared more towards inbound web connections coming over port 80/ 443/ etc? If so, you still require a unique port for the WC_defaulthost and WC_defaulthost_secure for each JVM when running multiple JVMs on a single OS install. But, the plugin file you generate for your web servers (based on the application mappings in the console) takes care of the redirection to the corresponding JVM based on the appropriate web server handling the inbound connection.