We have 17 RHEL 7 virtual machines running on 2 HP servers with ESXi. In order for Netbackup to successfully backup these virtual machines, is it true that a vCenter administrative account is needed? Or can it be done sans access to vCenter?
No vCenter account needed if you install NetBackup Client software on each VM.
You will need a Vcenter account with permission documented in Mariannes link.
Netbackup talk to Vcenter about snapshoting, removing and creating VM's. So yes, you need a account, but not nesseary a full admin account.
If you are using Vcenter in your environment, then Vcenter admin account with read and write permissions should be required for taking VM backups from NBU end.