The bpduplicate command is not specific to Unix. It's also present on Windows-based NetBackup media servers.
The short answer to your question is "yes". The bpduplicate command is used by NetBackup to create another copy of a NetBackup backup image. This can be a disk-to-disk, disk-to-tape, tape-to-disk, or tape-to-tape copy operation -- NetBackup doesn't really care about the specifics of the source and destination as long as both the source and destination are connected to NetBackup media servers. The source and destination for the duplication job don't have to be attached to the same media server as long as there is TCP/IP connectivity between the two media servers. The two media servers also don't have to be running the same operating systems -- the media server in Building A could be a Windows server and the media server in Building B could be a Solaris server, and it would still work.
The bpduplicate command can also be automated using the Vault add-on for NetBackup or by using the Storage Lifecycle Policy option (in NetBackup 6.5.x). Note that both of these options require additional NetBackup licenses. The Vault add-on is licensed based on the number of tape drives that will be used to perform duplications. The Storage Lifecycle Policy option is enabled by the "Standard Disk Option", "Enterprise Disk Option", or "PureDisk Deduplication Option" licenses, all of which are licensed on a
front-end terabyte basis (the amount of data sitting in your customer's client computers that they want to protect, not the amount of disk space in their VTLs or backup-to-disk appliances).
Your customer can definitely use bpduplicate to take backup images off of the VTL in Building A and write them to the LTO-4 drives in Building B. However, they should be fully aware that they will be sending the backup images over the 10Gig TCP Ethernet connection between the two buildings, which might have an impact on other TCP traffic that might be trying to use that same connection at the same time. They should also be aware that they might not achieve the highest possible speeds on their LTO-4 tape drives when using this approach, since the 10Gig link between the buildings might become a bottleneck.