This is how it works - as per SQL admin guide
About the NetBackup Discovery Service
The NetBackup Discovery Service (nbdisco) discovers SQL Server instances on
any clients that include the master server in their servers list. When NetBackup
installation completes, clients report their instance information immediately to the
master server. After this initial report, the discovery service asynchronously requests
updates from the clients. The clients periodically (every 4 hours) start their local
discoveries and send the information to the master server. The NetBackup Agent
Request Service (NBARS) polls the master server every 5 minutes and displays
newly discovered instances in the Applications > Microsoft SQL Server >
Instances node of the NetBackup Administration Console. If you enabled Auto
Registration, new instances also appear under the instance group that you use to
automatically register instances.
To discover the instances that you created since the last discovery, select Actions
> Discover Instances.
By default, this service reports to the master server when it finds instances of
applications. However, the user can turn off discovery for a specific client, with the
bpsetconfig utility.
See the REPORT_CLIENT_DISCOVERIES option in the following guide
https://www.veritas.com/support/en_US/article.DOC5332
