IU uses RHEL quite extensively, for a variety of projects. Many years ago, Gentoo was actually very widely used (much to my surprise).

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).