GroupWise Monitor originally came as an Agent (port 8200) and Application (integrates into web server). Recent versions of GroupWise no longer include the Application AFAIK, but if you've upgraded GroupWise over the years, it may have been left in place on your web server from an earlier install.

Here's docs on Monitor Agent/Application from GW8 for example:

This page also mentions the "Monitor Security Requirements" similar to your issue and suggest using a proxy server to control access from the outside.

I think that just removing the un-needed pieces is probably your only solution given that any install/uninstall routine for the Monitor Application are no longer available.