I guess by default, pre-defined (built-role) role such as "backup" is set to NONE for DEFAULT command/directory and cannot be modified. However, you can create a custom role and assign it to the user as necessary.
For example- According to the "section titled CDOT (NAS Backup Integration) for Veeam you shared", it requires following capabilities.
Create a custom role:
::> security login role create -role backup_veeam -cmddirname DEFAULT -access readonly -query ""
::>security login role create -role backup_veeam -cmddirname security -access readonly -query ""
::>security login role create -role backup_veeam -cmddirname "security login" -access readonly -query ""
::> security login role create -role backup_veeam -cmddirname "volume snapshot" -access all -query ""
::> security login role create -role backup_veeam -cmddirname vserver -access all -query ""
::> security login role create -role backup_veeam -cmddirname "vserver nfs" -access all -query ""
You can verify added capabilities:
::> security login role show -role backup_veeam
Create a user or assign the existing user the above role:
::> security login create -user-or-group-name netapp_veeam -application ontapi -role backup_veeam -authmethod <password/doman>
I don't know if this will help resolve it, but give it a try.
Definitions:
Command directory = Refers to a directory in the CLI.
Role = Refers to a collection of capabilities or privileges.
Access control = The capability is specified as an ‘access control’ on a ‘command directory’ or a ‘command’.
Related:
What is this DEFAULT rule and why is it getting created?
https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/FAQ%3A__Custom_roles_for_administration_of_ONTAP#What_is_this_DEFAULT_...