We use regular RHEL to run our Oracle database. When we were setting this up, several people pointed out that Oracle's Linux was doing some pretty horrible things to the kernel and overall system setup, so we stayed away from it.
As far as support, lets face it: Oracle doesn't provide support. You can open tickets with them, and maybe get pointed to a patch to resolve a problem. If you are not a database shop you will be working with an independent vendor, who will setup the DB and do a lot of the administration stuff for you. We're pretty happy with the guys we use, and they didn't care either way between Oracle's release or "true" RHEL.
The larger issue is, why not support ANY LSB compliant distro? I dislike RHEL for various reasons, I would much rather run Debian like I do everywhere else. However I can't because of the support contracts. It wouldn't make any difference to our DB support people or Oracle operation, but I wouldn't waste my time figuring out a different distro each time I have to do something on the DB nodes.