Sure, you can use OEL for anything you might want - but, the folks using this are probably folks using Oracle for the OS, applications, and possibly even hardware. What this means the Oracle *applications* are going to have better support and tuning.
The big news from Oracle is that it's offering a "modern" Linux kernel that's supposed to offer better performance and support for newer hardware (like solid state disks), and is optimized for Oracle hardware and software.
In practice, it works out something like this. Lets say you call up with some sort of goofy DB or Weblogic issue. Support *has* your exact environment. The application developers may have also used that same environment for development, making this the 'native' build rather than some other platform that the codebase was ported to. It also sets the bar on what you can do with some of the newer kernel features. Sure, you could custom tweak your own kernel to get some goofy bit of hardware to work, but if it breaks the app and you have to call support... Think of it as more of a least common denominator for the Oracle dev folks.
RHEL, OEL, and CentOS are all the same bloody codebase. Thank $DEITY. Pick your support contract vehicle on the commercial side. The fact that commercial applications run very nicely on that cut of Linux is one of the reasons Red Hat has the following it does. (I've got Red Hat in my dead pool for companies to be acquired - I'm surprised something this strategic remained third party this long.)