In addition, you may also need patent indemnification and reliable security updates (we leaned on Red Hat heavily during ShellShock and others). For example, before I release a Linux image I have a checklist of 450+ items, including things like NIST certification. Red Hat streamlines this process as it has already been certified across the most strenuous of regulatory and compliance environments, and we can reuse much of that work.
This isn't important for a clothing website startup for example, but for aircraft, CT scanners, anything ISO compliant, finance it is paramount to what is being delivered.
RedHat's userbase is basically the opposite side of the spectrum from Ubuntu users flying by the seat of their pants with that popular free server thingie they heard about.
Amazon Linux is based on Redhat. CentOS is a Redhat recompile, so you can say anyone using that is also using "Redhat". US govt almost exclusively uses RHEL when they mean "Linux". Also banks, healthcare, etc.
It seems to be by far the most popular version used by governments and large corporations.
"We're an enterprise software company. You're either consumer or enterprise. We're enterprise."
I would assume Redhat-required shops would be running some pretty heavy, sophisticated workloads.
If you want support from Oracle and you're not running on RHEL or Oracle's own offering, the answer usually is, "Get back to us when you can reproduce it on a supported flavor of Linux."