Red Hat used to release its kernel SRPM package including a tarball of the vanilla kernel sources and a set of custom patches. This made it possible to rebuild the kernel with or without patches or with a custom selection of patches. It seems that things have changed and Red Hat now releases the Red Hat Enterprise Linux kernel source already patched. This basically makes things less flexible for those who wish to apply a custom selection of Red Hat patches to the vanilla kernel source or build upon Red Hat’s patches and create derivative works.
It is quite clear why Red Hat makes this move. It doesn’t want to provide its work on the kernel free of cost to those companies that make commercial rebuilds (see Oracle Enterprise Linux). I won’t try to criticize this move because I don’t see any valid reason for criticizing this business decision. Personally, I don’t think it complicates things more for CentOS and Scientific Linux, since there is no kernel development taking place in these projects. On the other hand, it might have a negative impact on any cooperation on the kernel development among the various Linux distributions.
There is an ongoing discussion about it at LWN you might find interesting.
The RHEL kernel source released with patches already applied by George Notaras, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.