They’re a pretty big contributor to Linux, so even if you don’t see their work you’re probably using it anyway. lwn.net/Articles/915435/
added value that cannot be fulfilled by independent experts or FOSS community
Wrong question IMO. It’s more relevant to ask “without Red Hat, would independent experts or the FOSS community have added the same value?”. Sure, it’s possible that Red Hat has some highly skilled developers that possess unique skills required for their contributions, but in general contributing to FOSS projects is more about willingness to spend large amounts of time and resources on something that doesn’t give you money in return.
Lots of large companies “could” have spent thousands of hours contributing to Linux, but unless they actually do it then it is irrelevant.