Note - I contacted the plugin author and they were quick to reply, and their reply was everything you would want. They are a class act.
We've been reviewing this plugin and just are amazed at how it exposes stuff going on that we had no other way to see. Life was good until we installed this plugin on a site that also used WP Mandrill.
I thought this was a sneaky enough problem, that I wrote up the problem and how we found it on our website WPMandrill Plugin – WP_Mail Conflict
In a nutshell, WP Security Audit Log calls pluginable.php and then WP Mandrill tries to define wp_mail, which was already defined in pluginable.php. So I hope that the developers of WP Security Audit Log can do their magic and let the two plugins co-exist.