This won't prevent them from crawling the board or reducing the number of registrations. I've eliminated bots spamming my board since I started requiring email validation on all accounts. They don't respond to this, and you can just delete the "Awaiting Validation" accounts at your leisure.
However, this link should just need to be placed on your board's default skin, as that's the only one that the spambots (using Guest account) can actually see.
