I tried the Google Site search and it works fine on the forum.
Example:
site

//forums.eunuch.org androcur
Leave everything before the "androcur" and replace androcur with your search term. The sub domain "forums.eunuch.org" is archived by google.
It's true that google won't index sites behind a password. But, the sub domain forums.eunuch.org doesn't require a password to read it - just to comment.
I looked for any instructions that would tell search engines to not index this site and found none.
The main page of eunuch.org request that spiders (the robots that index websites for search engines) only come back every 15 days:
<meta name="revisit-after" content="15 days" />
But, the page makes no request that robots stay away or not follow links and index the site.
On the main page there is a robots.txt file (sort of a backup to the meta data) which does request that robots and spiders not follow to the directory called "forums":
User-agent: *
Disallow:
Disallow: /cgi-bin/
Disallow: /forums/
Disallow: /personals/
But, obviously Google doesn't read that as a prohibition for archiving the sub domain. I'm not sure if Google would see "eunuch.org/forums" differently than it sees "forums.eunuch.org".
So, I looked at the meta data on the sub domain of "forums.eunuch.org" and there is this tag:
<base href="
http://forums.eunuch.org/" />
If that was supposed to tell Google to look back at the meta data and robots.txt on the "base", it didn't work (I'm not familiar with that meta data tag and really not sure why it's there. Maybe to help the database find the mysql file?)
Lastly, there is no robots.txt file in the sub domain of "forums.eunuch.org" and I think that's the reason Google archives the forum.
Since the sub domain is available with a direct url entry, Google will find it and look for a robots.txt and any meta data that asks it not to index. Google will honor the request if it finds it. Not all search engines honor the request.
I'm not sure it's ever been discussed if the community wants the site indexed by Google. Then again, the horse might be out of the barn by now and locking the door would be pointless.