As of the August 2017 Apple School Manager update, the ASM MDM Class Roster API now includes email address and SIS username for a given ASM user.
Please allow user matching based on username and email address.
As of Jamf Pro 10.2.0, the SIS Username and Email Address fields from Apple School Manager will sync with Jamf Pro Users. These fields are available in the Roster tab of each user imported from Apple School Manager. These fields have also been added as matching criteria for the user import processes. Please let us know if syncing these fields with Apple School Manager have helped solve the problems we were struggling with. We look forward to the feedback!