What exactly is the device in Data Protector you are backing up to?
Because it sounds like your cell manager is your VADP backup host for the integration, which means it's also virtual.
Thus it cannot talk to any Fibre based devices since ESXi has no support for any medium changer or tape drive SCSI class devices over FC. Is this an iSCSI VTL?
If the VADP backup host is physical, you can use the SAN transport. If the VADP backup host is virtual, it'll try and use HOTADD. I don't care much for the idea of a virtual backup host. You can try NBD but make sure access to port 902 on the ESXi server is not blocked.
You need to figure out if you're talking about a VE integration issue or a device issue. The longer you keep mixing the two subjects, the longer it'll take before you can make any progress.
Thanks,
Scott