Well, Red Hat Enterprise Linux 3 is based on Red Hat Linux 9. FC2 is thus a bit new for today's RHCE exam.
If you're planning to wait until the Red Hat Enterprise Linux 4 exam is released, use FC3. Red Hat Enterprise Linux 4 will be based on FC3, and word is (
http://linuxtoday.com/it_management/2004113001826NWRHSW) that the new operating system will be released Q1 2005. Historically, the exam has been updated within 2-3 weeks of the operating system release.