I don't use RH at the moment, so this isn't directly relevant to me, but I have to wonder why someone isn't already designing a tool to take a monolithic patch and search a git repository for matching changesets. Seems like it should be reasonably straightforward (even though it might be slow). Even if the results weren't 100%, such a tool could probably identify a substantial number of the public changesets incorporated by RH in their kernels, leaving a much smaller chunk of unknown patch to deal with.
(This might not help in a case where someone keeps all their changes private, except for a monolithic patch, but as I understand it, RH does push pretty much all of their changes upstream to git in some form or other, and the only real question here is which specific changesets they're using in a specific kernel binary.)
If this isn't happening simply because people still have more respect for RH than for Oracle, and would feel uncomfortable undermining RH to possibly benefit Oracle, despite distaste for RH's current actions, then I understand (that's actually a part of why I haven't looked into it myself).