Ever heard of plausible deniability? I can assure you that Fedora is just as much a Red Hat distribution as RHEL is, maybe moreso. Fedora is Red Hat's playground. RHEL 4 will essentially be Fedora Core 1, hide and watch. RH made a lot of noise about community development, but Alan Cox, Warren Togami, Arjan van de Ven, et al are still firmly in charge on the Fedora project.
Huh core one was kernel 2.4, RHEL4 is 2.6... they have different gcc levels, different X levels (hell core one might have been XF86, where RHEL4 is Xorg. if RHEL 4 is anything is might be Core3. All of this is besides the point as RHEL is spinning off Fedora..