If a user matches a "useragent" they will be defined as a bot; this setting is completely independent of spider friendly URLs and simply means that a bot is accessing at least your homepage.
Spider Friendly allows spiders an easier route of transversing your webspace; nothing is to say they will be completely blocked, but nothing guarantees they'll have an easy route of spidering your forums.
Another benefit of Spider Friendly is that your URLs to posts will be MUCH shorter.
