Yes, the admin can be a master calibrator. In addition to this role, the admin can:
Create sessions, thus becoming the owner.
Be a participant in the session.
Serve as the master calibrator.
Delete sessions they own.
Important: Admins have the authority to manage and edit Calibration sessions they own, not of anyone else.
Check here, how you can add a master calibrator to a QA Calibration session.