has a method to keep the newest user at the bottom of the board from showing inactive users. This post
will keep the memberlist from showing inactive users unless the person viewing it is an admin. The post right below that shows how to make the number of registered users reflect only active users. I coded all those into my board and they work fine.
So if bots register at your board they will not be seen by the general user populace if you also have either user or admin activation. You, as admin, will still be able to go into the member list and see if any bots have signed up and therefore you can go in and delete them. If you have a large number of those I would suggest the Admin User List