Nothing has changed with Red Hat. While technically, it would make more sense for Oracle to partner with Red Hat in supplying/supporting Oracle customers' operating systems, Oracle obviously thinks that it is leaving money on the table if it doesn't own the stack, from application to OS. The money and owning the entire stack are two good reasons, as far as Oracle is concerned. Certainly there is a tendency for application vendors to provide the entirestack: suppliers and customers both seem to think there are fewer problems and less finger-pointing that way.
Red Hat continues to be an important kernel developer and maintainer. Oracle, no matter how many developers they poach from Novell (I'm more concerned about SUSE than about Red Hat), has not yet attained parity with Red Hat as a distro supplier.
What you pick will depend on your situation. You evidently demand a serious system, since you are considering RHEL, and have the money to buy support. You'll have to do your own evaluation on the support reputations and pricing of IBM (several distros), Novell (SUSE), and Red Hat. If you are looking for a distro that is far from the present controversies of Red Hat and SUSE, Ubuntu has an amazing reputation and Canonical offers commercial support ($250/desktop; $700/server). While the praise I have heard comes from individuals rather than commercial users, I understand that Ubuntu is now certified by IBM to work with DB2.
Xandros moves quietly in the commercial world, and also offers a server product. But as in the case of Ubuntu, I can't think of any enterprise users of the distro.
Think some more about Red Hat. I don't think their serious customers are going to go rushing over to Oracle.
This was first published in January 2007