Indiana University uses Red Hat for Carbonate large memory cluster. I’m sure many universities still use Red Hat for various projects like this.
Once IU got a site license for RHEL -- one of the first .edu's to do so, IIRC -- they pretty much standardized on that. In addition to all "official" University systems, their RHEL license also covers personal systems for faculty, staff, and even students (my first "real" RHEL boxes were registered to their newfangled Satellite server).