Chris, AFAIK ..no. Unless there is a way you can merge the media and image database catalogs of BE with NetBackup (a process I'm sure does not exist); you have to import/catalog your media, otherwise how will NetBackup be able to browse backups for restoring, when using the BAR software.
Some thoughts:
You might have a think about the data you have offline on BE tape media currently. Its importance, the retention you have on the images on the media. How often are you requested to perform restores. And the SLA time to restore.
What I'm saying is that keep your BE server. But migrate to NetBackup - clients and hardware. Worse case scenario you have to remove a tape drive from NetBackup config and rezone/present it to BE server - its time consuming but if you can only import 1 media at a time and you have 100.
Unless your BE media retention is based on 12 months and more, you could purchase some more tapes, remove all the BE media from the library. Use the new tapes in NetBackup, and over time if your BE media expires inventory them into NetBackup for use.