.... plus straight from the Admin Guide:

Symantec OpsCenter This OpsCenter version does not require any license.
Symantec OpsCenter provides single deployment configuration and user
interface for monitoring, alerting, and reporting functionality. These
features were previously available in NOM and VBR.
Symantec OpsCenter Analytics is the licensed version of OpsCenter.
In addition to the features available in the unlicensed OpsCenter version,
Analytics offers report customization, chargeback reporting, support
for third-party data protection products, and also NetBackup Search.
The NetBackup Search functionality is now also available with Symantec
OpsCenter Analytics 7.5.
If you upgrade from an earlier version of Symantec OpsCenter Analytics
to 7.5 and want the Search functionality, a new OpsCenter Analytics
license key can be purchased which enables only the Search functionality.

Note: OpsCenter 7.5 does not support upgrades from NOM and VBR.