Just to clarify and quantify... what exactly does Red Hat contribute to?... here's their list:
https://community.redhat.com/s...
Not only do they contribute by funding development here and there, they have created many projects themselves and sustained them until they successfully made them into an upstream community. I'm not sure where to find that list but it is a subset of the above link. Any of the upstream project web sites that have a "Powered by Red Hat" type logio in the top right is a good indicator.
Red Hat over the years also purchased / acquired a few handful of companies... and if those companies already had open source products, they remained open source... and if those companies had some proprietary products, in most all (if not all) cases, even though it took quite a bit of work... over time those proprietary products were opened up... and upstream projects were created for them. Red Hat Directory Server used to be Netscape's proprietary product but is now upstreamed as 389. Quranet's SolidIce management system was all Windows server/technology-based and although it took a couple of years to completely re-write it in Java... it became RHEV and later RHV... and upstreamed as oVirt. The list goes on and on.
Then there are the big Enterprise class products Red Hat started from scratch and then over multiple releases adapted to use other's technologies where appropriate (they aren't afraid of not-invented here) like with OpenShift. At first they had their own container like entity that was called a "gear" and mostly namespaces, cgroups and SELinux policies strung together. Then they adopted Docker... and later Kubernetes.
When they found issues with the development model of Docker Inc, they started developing completely open alternatives like podman, buildah, skopeo, etc.
In any event, their story has always been combined with Free and Open Source software and believing in it. They did have one challenge when they made their own Red Hat Network backend based on Oracle DB... but that was fixed over time and eventually completely open sourced for use with other databases... and even forked to be used as a commercial product by SUSE.
And then there was the whole Oracle Enterprise Linux fork of RHEL... and CentOS... (in no specific order)... and their eventual sponsoring of CentOS. And of course, don't forget Fedora. It took them a while to get to Fedora but they did.
BTW, a commenter's mention of systemd... Red Hat did not originally agree with the idea of starting systemd... but Lennart P. continued developing it on his own time... and got it into Fedora and it proved itself... and was eventually adopted by RHEL... but it was never a given. Some people think systemd is a cancer others really appreciate the wide range of features it enabled (welcome modern world!)... and still others seek to emulate it on other OSes. One thing is for sure, systemd makes sysadmin easier to teach, learn and do across all of the distros that have adopted it.
I'm sure there are many developers who have gotten paid by various companies to write both proprietary as well as open source applications on top of RHEL... and to sysadmin RHEL... and to devops it... and to support it... as an alternative to Red Hat's paid support. It has created all kinds of opportunities outside of RHEL and their various other products. As previously mentioned a whole lot of that work has made its way into the greater Linux and FOSS ecosystems and is enjoyed by pretty the vast majority of Linux users everywhere.