I was fishing for ideas and I randomly decided to paste https://SERVER:8443/principals/wikis/wiki-GROUPNAME into firefox and discovered all the XML goodies that resided within.
So I started looking all around on what folders I could find. I then thought . o O ( I can see the Group Calendars when I subscribe to the them so what if I use that address )
Sure enough when I used uids/wiki-UNIQUEGROUPID__wiki_guid/calendar/">https://SERVER:8443/calendars/uids/wiki-UNIQUEGROUPID__wiki_guid/calendar/ I found the .ics files for the calendars and was able to download them and view them in iCal and verified they are the same as what was on the wiki.
Also, I found the XML entry: {DAV:}current-user-principal: /principals/wikis/UNIQUEGROUPID__wiki_guid/
Knowing which Principal was assigned to the calendar was the critical piece for me as I was then able to open iCal and add a CalDAV account for: https://SERVER:8443/principals/wikis/UNIQUEGROUPID__wiki_guid/
Sure enough I can now view and edit Group Calendars both in iCal and Wiki Server.
I hope that others will find this information useful, because I read online that the feature is not supported which was confirmed when I contacted AppleCare directly. And it is not well documented through any searching that I did.
I suppose there is a risk however and this should act as a disclaimer, that the feature is not supported by Apple and therefore any future updates to the XServe may prove to disable the feature again. Which is terribly unfortunate because the feature is so critical to our professional resources.