When adding an Azure account to Veeam Backup & Replication, you would use the Add > Microsoft Azure compute account... then, on the Subscription tab of the wizard that opens, select the "Create a new account" option. Doing this will register a new Azure AD Application. The account used to register the AD Application has to have the appropriate permissions. For more information, please review: Adding Microsoft Azure Accounts in the Veeam Backup & Replication User Guide.
If you prefer to set up a custom role for Veeam Integration, you can use Azure PowerShell method to create one.