How can I configure fail2ban for use with OS X I've seen instructions for configuring fail2ban on BSD using pf but I'm not sure how these can be adapted to configure the fail2ban rules that ship with homebrew to configure Yosemite's firewall for safety.

What changes do I need to make, and to which files, to enable fail2ban safely on my OSX server?
If you are running the macosx server product (as well as running macosx as a server), you can try activating the adaptive firewall (man afctl(8)). It is a tool that watches for auth failures and blocks the originating host for a short time. Not quite as flexible as fail2ban but catches some of the services that don't log auth failures.