Hi,
I do not see a reporting feature for this currently.
The Incoming Mail report does track graymail received per user, however nothing for safe unsubscribe as the action is performed after the email has passed through the ESA.
https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/200383-Graymail-Detection-and-Safe-Unsubscribin.html
Thank You!
Libin Varghese