The VAS install guide advises that HP-UX systems need to be rebooted when upgrading VAS, is this actually required?
You can't delete a file on HP-UX that is being used by an existing process - you can only move it. Existing processes will not use the new VAS libraries until they are restarted. When you remove a package in HP-UX, if any of the files are in use, they are locked and can't be removed and are instead renamed. There is a "cleanup" script that runs on reboot that will remove these renamed files.
In most cases, you should be fine, without rebooting, if you just restart processes like SSHD that may be using the existing PAM/NSS libraries, but it may depend on what applications are running on the system. HP-UX can be problematic with how strict it is on files-in-use-deletion.
It has been further noted in certain environment that the upgrade procedure can result in "hanging processes" on a HP-UX system. If you suspect that you are experiencing this it is recommended that you un-install the version of VAS that you upgraded to and then install the new VAS version directly. Due to the above file-locking on HP-UX, it is also typically recommended that you reboot the system after installation.