Keep in mind that a lot of Red Hat employees use their personal email addresses when committing to the kernel. It has always been allowed (though not necessarily encouraged), and many developers were involved in those communities before (or plan to be after) working at Red Hat, so they use their own email for continuity sake.
Especially if contributing to the kernel is something they only do infrequently rather than as part of their day job.
I believe that the LWN folks take that sort of situation into account, they don't just use the email address domain as an indicator of employer. And of course RedHat people probably do some Linux kernel work outside of paid time if they have pet issues unrelated to their RedHat directed time.
Especially if contributing to the kernel is something they only do infrequently rather than as part of their day job.