Just to make things work, you need only one licenses for all client related activites installed on your master server. Legally, you are responsible for tracking it and with current version of NBU there is no way to keep track, except the manual work (count clients/DB policices/Advance client policies etc). I know Symantec is working on a new product SLIM, to do this kind of job and they have bundled it with NBU 6.5 but at this time I am not sure if it is really doing what you are looking for or not.
NetBackup installation enhancements
A new package install SLIM agent
The Symantec License Inventory Manager is an asset-management tool that
tracks the Symantec products that are installed and deployed in your system.
The Symantec License Inventory Manager does the following:
■ Inventories all Symantec product software that is deployed in your network
■ Collects and consolidates critical license information about those
deployments, including but not limited to the following:
■ Product name
■ Product version
■ License type
■ License expiration date
■ Installed license keys
You can compare this information with your license purchase records to help
manage your license compliance