Not really. RHEL / CentOS is basically a hardened snapshot of Fedora taken every few years, with a few bespoke changes on top. So in that sense you could argue that Fedora is a front-runner for "the next RHEL" but at any point in time it is too far ahead of the current RHEL to be a useful testbed in any respect for those users. Although I guess you could argue that it helps knock down bugs in packages like GNOME that do get updated regularly in RHEL.

CentOS Stream is basically "the next x.y release of RHEL". Some updates, like GNOME updates and new hardware enablement, will be present in CentOS Stream a few months before they are released to RHEL and CentOS as part of a new x.y-release.