Intended - yes
In practice - mostly
There are cases out there where applications intended to run on a RHEL distro will not install without modifications. The distributions, although based on the same sources, are not the same. There are applications out there TODAY that won't install or run correctly on CentOS but will install and run correctly on RHEL.
RHEL is not self-hosting - in other words, it's possible that the binaries you get can not be built with the sources you get. That's happened in the past due to compiler bugs but I haven't heard of it happening lately.
CentOS, as a client, is supported by Symantec according to the current compatibility list at
ftp://exftpp.symantec.com/pub/support/products/NetBackup_Enterprise_Server/337048.pdf. It's not supported as a master or media server. We don't know if it's because they tested it and it failed, or if they tested it, it worked but they don't want to support it, or they simply didn't test it.
In general, I would expect that you could make a NBU 7 master install on CentOS and it would likely work. It will not be supported by anybody.
Depending on the tier of the hardware that you're running the master server on, the list price for the x86-based Linux master/media runs from $5K to $12K and that doesn't cover any clients or options nor the backup hardware or media. A RHEL subscription can be had for $349 per year.
My personal opinion is that the $349 per year should not break the business case.
.../Ed
Disclaimer: I'm a Red Hat Certified Engineer so I obviously have some bias to go along with my experience.
