The bottom line is that CentOS is now a second-class citizen with regard to support from KSplice, compared to Ubuntu and Fedora. See the KSplice download page at http://www.ksplice.com/uptrack/download in which CentOS is missing.
Regarding the source code, yes the original code was GPLed is still available. But are you saying that Oracle/KSplice will continue to make available ongoing versions of KSplice?
The link you provided is to a source tarball that was mostly last updated in August 2009, except for a small change in July 2011 (removal of zlib detection). Therefore, either the KSplice code is not being maintained at all, or there are ongoing updates to it that will no longer be released in source form.