1. Redhat Linux release is now know as Redhat Enterprise Linux and is fully supported by Redhat and its release started with version 1. Whereas 
Fedora is a Redhat unsupported release.
2) Redhat Enterprise Linux is a tested version and are extracted from fedora. Whereas fedora is a testing bed where all are allowed to put their codes, knowledge, etc to develop, which if good is put in fedora.
3) Redhat costs you, whereas Fedora is free.
4) There is certification on RHEL Whereas on fedora there is no certification