To enable backup from storage snapshots with a Nimble Array, it is necessary to add the storage system to the Veeam Backup & Replication console's Storage Infrastructure. This allows Veeam to interact with the Nimble Array and orchestrate the creation of storage snapshots, which can then be used for backups. Simply enabling the backup from storage snapshots option in the job is not enough; the array itself must be integrated into the Veeam infrastructure.References:
* Veeam Backup & Replication User Guide: Integration with Storage Systems
* Veeam Best Practices: Nimble Storage Snapshot Integration

To ensure that all servers for the accounting department are backed up and any new servers added to the department are automatically included in the protection group, the best approach is to use an Active Directory (AD) based protection group. Therefore, the correct answer is A:
Create an Active Directory based protection group targeted at an Active Directory security group.
By leveraging an AD-based protection group, the Veeam administrator can specify an AD security group that encompasses all user accounts or computer accounts (in this case, servers) associated with the accounting department. As new servers are introduced and added to this AD security group, Veeam Backup & Replication will automatically detect these new members during its periodic rescan (which can be scheduled as per the administrator's preferences) and include them in the protection group. This method not only automates the inclusion of new servers into the backup routine but also simplifies the management of backup policies for dynamically changing environments such as the accounting department's server infrastructure.

For a VMware environment on a Fibre Channel SAN, the most efficient proxy transport mode to minimize impact on the production environment is Direct Storage Access. This mode allows the backup proxy to directly interact with the SAN, bypassing the production network and reducing load on the ESXi hosts.