Yes, you can, but you need to verify that Linux Client software is installed on your master.
By default, only Client software for master's own OS version is installed (HP-UX in your case).
To check, go to /usr/openv/netbackup/client/Linux folder on your master server.
List contents and find the folder that corresponds with your client's OS, e.g. RedHat2.6 or RedHat2.6.18.
Check contents of this folder. If it is empty, it means that the client software is not installed on the master.
If you see files in this folder, check the contents of 'version'.
For example on my 7.5 master server, I see the following in version file under RedHat2.6.18 folder:
/usr/openv/netbackup/client/Linux/RedHat2.6.18 >cat version
NetBackup-RedHat2.6.18 7.5.0.3
If your Linux folder is empty, you need to install Linux client software on your master.
See instructions in the Installation Guide under this topic:
Adding a UNIX client after initial server installation