Acredito que você pode chamar
sys.fn_my_permissions
:execute as user = 'SomeUserName' -- Set this to the user name you wish to check
select * from fn_my_permissions(null, 'DATABASE') -- Leave these arguments, don't change to MyDatabaseName
order by subentity_name, permission_name
revert
Isso me deu os mesmos resultados que a opção SSMS que você mencionou.
