How can I monitor for bot accounts accessing drupal paths without permission?
You could try adding bot protection to your registration form, 

e.g with reCaptcha

Other worthwhile things are blocking the bots in your webserver, 

e.g nginx 


https://github.com/mariusv/nginx-badbot-blocker or 
https://github.com/oohnoitz/nginx-blacklist/blob/master/blacklist.conf 


Custom options include using the Flood control API, 

e.g flood_is_allowed and flood_register_event with ip blocking (e.g system_ip_blocking_form_submit) or user_block_user_action on the node/add or 403 page.