Red hat provided the source to their kernel with the letter but not the spirit of the law, to impeed Oracle Linux. We'd (Ksplice) get the changes from Redhat version to version as one giant patch file, with all the changes mixed together. There's no chance in hell their internal kernel developers worked that way, but the source was there, so the letter of the GPL was satisfied.
The other thing they did was close the source repos. First you had to be a subscriber to get the binaries, and thus by the GPL, you could get the source. However, if you shared that source code with anyone else and they caught you, they wouldn't let you renew your license the next year, so you couldn't get the newer version, binaries OR source. This also isn't technically against the rules of the GPL, but it's hard to see that as being in line with the spirit of it.
It's hard to see Redhat as the benevolent GPL open source hug supplier with real world business practices like that. Not that I fault them for it, it's just business.