Hello David,
There is an upgrade path for either VBR or NOM which will consolidate both apps into one interface.
If you have custom reports built in VBR, then upgrading VBR to OpsCenter will "upgrade" your custom reports so you won't have to rebuild them in OpsCenter afterwards. I prefer to run VBR on a Unix system, I ran the upgrade to OpsCenter on Solaris to keep all the reports I had already been using. We have a NOM installation on another Solaris server, but only use it in a very minimal capacity - making it easy to recreate the few things we have setup.
The good news is even after you run the upgrade to OpsCenter (installing in a different directory, you can still run VBR if needed. If OpsCenter is haivng issues for some reason, you can stop the services and fire-up VBR and you're back in business, (you cannot run both at the same time). I hope this helps.
If you have anymore questions, please let us know.
Cheers,
Rick