Well, the spider list is just to identify spiders in the Who's Online page (otherwise they show as "guests"); updating this list will do nothing to alert spiders of your forum (though my UBB.SiteMaps modification will aid in feeding urls to search engines that support sitemaps).
As for the CI, your code looks fine, if you're setting this up to be a post island (inbetween the first and second post) you'll need to make sure that the group permission to see the ad in each forum is also set to 1
