Sysadmin here, currently studying for RHEL certs. All I know from what my coworkers have said is that its pretty tough.
I've managed RHCE and RHCVA, and I can say that primarily they're different from other industry certs, rather than being more or less tough. On the one hand, they're all practical, so you don't need to have "the right answer", you just need to know how to accomplish tasks (one way or another). On the other hand, the diminished number of questions/tasks means that each counts for significantly more. One very nice thing though is that you have access to all the man pages, which are definitely invaluable.