Have You checked if the file system created on this LVM is supported by NBU??
For NBU 6.5. here are the supported file systems:
OS Platform File System ACL Extended Attributes or Named Data Streams Notes
Red Hat Ext 2/3 Yes Yes RHEL 4 kernal and later for x86, x64, IA-64. Initial support with NetBackup 6.5
Red Hat VxFS Yes Yes (VxFS 5.0 +) VxFS 5.0 is x64 only on Linux. Initial support with NetBackup 6.5
SUSE SLES Ext 2/3 Yes Yes SLES 9 kernal and later for x86, x64, IA-64. Initial support with NetBackup 6.5
SUSE SLES Reiser, XFS, NSS Yes Yes SLES 9 kernal and later for x86, x64, IA-64. Initial support with NetBackup 6.5
SUSE SLES VxFS Yes Yes (VxFS 5.0 +) VxFS 5.0 is x64 only on Linux. Initial support with NetBackup 6.5
Taken from ftp://exftpp.symantec.com/pub/support/products/NetBackup_Enterprise_Server/325328.pdf