I haven't found anywhere in the Google's Android Management API any alternatives to using Google Cloud as its backend.
For users who have hard requirements against using Google Cloud or if it's unavailable in your physical location, does Google provide alternatives?
For context, Apple's take on this is that infrastructure is provided by the user itself and there is no "middle man".
The alternative option that Google provides is the use of Google Play Console. It allows users to use 3rd-party identity service by linking managed Google Play Accounts with the user’s existing identity accounts.
Also, since this is not tied to a user’s existing domain, creating more than one Enterprise for a single organization is possible.
Please refer to this link for additional information regarding this matter.