The admin role is required to impersonate any user in ServiceNow, while the impersonator role is required to impersonate a user who has granted impersonation access to the impersonator. The other roles are not related to the impersonation functionality.
References1: Impersonate a user - Product Documentation: San Diego - ServiceNow2: Non-admin users with the "impersonator" role cannot impersonate any user if there are orphaned 'sys_user_has_role' records like "
[user: null; role: admin]". - Support and Troubleshooting - ServiceNow