Setting a user without any password as an administrator would not provide the security I believe you desire. As an admin will need to perform the backup as well as they will have the ability to manage users and view all workbooks as they need this level of permissions to perform the backup.
As for an automated way to backup Tableau Server on Linux, the process can be scripted, using the following ; Back Up Tableau Server Data
Hope this helps!
Thanks for the input. The link you provided below however doesnt really help. I've previously read this page and tried it but when running the 'tsm' commands I get prompted for a password to authenticate the user. This is the stumbling block I am trying to get around in order to automate a backup