I've a system that has numerous RPMs with the label .fc6 - but it is an RHEL 5.4 system. It is not impossible that it was updated from CentOS 5, but can't be certain. Others are labeled with .el5 and some with "jpp" - but most have no such suffixes.
It also has numerous dual architecture items loaded, with i386 combined with x86_64.
Does RHEL contain Fedora Core packages? Does CentOS contain Fedora Core packages? Whatever for? What is JPP?
Update: Looks like jpp packages might be from JPackage.