Er, on what grounds? RHAT is perhaps doing the bare minimum required by the GPL - but they are doing it.
What this does does not prevent Oracle from recompiling the kernel and running it, nor does it thwart studying the kernel, etc. It just means that they have to do detective work to figure out what's changed and where. Unless I'm mistaken about the GPL, there is no requirement whatsoever to provide any commentary on changes or break changes out as patches from the original source - only that you have to supply the changes, which they've done, but as part of the overall kernel.
I can't see Oracle having any cause to sue, even if they are (I hope) inconvenienced by this.