It's essentially a development release rather than being explicitly labelled "rolling" (and, in fact, its use as a day-to-day distribution is generally considered A Bad Thing if you're not a Slackware developer/tester). It just happens to have the bonus of also being a pretty bleeding-edge, yet stable rolling release.
So, it's possible to achieve both a rolling release and "stable", versioned releases.
Honestly, Slackware is almost a RHEL/Fedora type ecosystem when just taking about official packages. Slackware-current gets new stuff, Slackware releases only get bug fixes, and not too many of them at that.
Basically yes, Fedora is Red Hat getting free testing of features and when it's time to create a new RHEL release, they grab a Fedora release, set it in stone and work from that.
http://en.wikipedia.org/wiki/Red_Hat_Enterprise_Linux
Red Hat Linux 6.2 → Red Hat Linux 6.2E
Red Hat Linux 7.2 → Red Hat Enterprise Linux 2.1
Red Hat Linux 10 beta 1 → Red Hat Enterprise Linux 3
Fedora Core 3 → Red Hat Enterprise Linux 4
Fedora Core 6 → Red Hat Enterprise Linux 5
Fedora 12, 13 → Red Hat Enterprise Linux 6
RHEL trees are forked off the Fedora repository, and released after a substantial stabilization and quality assurance effort.
Which adds a quote from the Fedora Project:
Red Hat Enterprise Linux is a commercial enterprise operating system and has its own set of test phases including alpha and beta releases which are separate and distinct from Fedora development.
And on that page[1] it states that RHEL6 is based on a "Mix of Fedora 12 Fedora 13 and several modifications".
Sorry to be pedantic, but that's significantly different than the Slackware model. Maybe it's just PTSD; I fled from RH in the old days onto the path that led to Slackware, so any comparison makes me touchy.
[1] https://fedoraproject.org/wiki/Red_Hat_Enterprise_Linux?rd=R...