By design SmartZone will not let you use a custom credential with super-admin permission on CLI/Console - either through external management servers or internal database.
SSH / CLI only accepts "admin" as username and the password associated with admin.
This only applies to the CLI (SSH) and Console. The Web UI does let you use LDAP/Radius/AD.
Applies to 3.x, 5.x and 6.x SmartZone versions.
Cecil D'silva | Staff Engineer |Technical Support