There's nothing sitewide in place for filtering this, so any iceberg syndrome would only be from built-in filters in your CMS. As such, I'd say you should give the word-based filtering in that article a go. I don't think it can hurt. I'm not sure how many of those directives are allowed in .htaccess, but I'd imagine the ones in the top code block (aside from CustomLog... individual users don't have authority to mess with sitewide logs) should work. I've not dealt with this sort of spam before, only erroneous forum posts and the traditional email kind, so I'm afraid I'm a little light on advice for you. One question is if this spam is going to your custom-made (willow?) CMS, or your blog/other CMS? If it's not willow, which CMS system and version is it using? Also, are they targeting a particular page/file, or just broadsiding the whole thing? Often you can rename some of the scripts so the spambots don't recognize it as a known CMS. E.G. mt-comments.cgi becomes mtcom.cgi.
If you have any questions or need some help, let me know. I'm sure we can find a way to stop it.