of course your raw logs from cpanel, plesk or whathaveyou will show them visiting your site, remember this mod redirects them when trying to load your site, it does that regardless of whether they are trying to load the homepage or a thread, your Alexa shouldn't drop on account of redirecting spiders, in fact i've been redirecting these spiders for ages on one of my sites that was Page Rank 2 and it's now PR3, so if it's not hurting Google rank it has to be good
Can you give me a screenshot of your settings for ths mod?