I was looking where is this written and I fount only this technote:
At the bottom of the technote says
Note that this problem is not be present in NetBackup 7.0.1 and higher as vnetd and bpcd run standalone and the inbound connections are not received via xinetd.
No its not required. As StefanosM mentioned, NetBackup doesn't use xinetd for its installs since 7.0.
You can refer to this tech note for more information: http://www.symantec.com/docs/TECH135628