OLE does not exist. Perhaps you meant OEL, but then again the product changed. There are plenty of technical reasons to use Oracle Linux (OL) instead of RHEL or CentOS, etc. in particular if you plan to install Oracle database or use Oracle cluster or ASM. There are Oracle specific software products and kernel drivers that are only available using the Oracle UEK kernel. Whether or not RHEL would become free too has no impact. Oracle is not a thread to Linux, actually less than Red Hat Enterprise Linux since it is free and you don't have to pay to receive updates. Personally I lost interest in RHEL when it turned into a commercial product about 10 years ago. You can't even download or register to try RHEL unless you have a corporate email account.

You don't need ZFS anymore. The latest version of Oracle Linux supports BtrFS, which is also GPL and fits Linux licensing.

Oracle does not support ASMLib, OCFS2, etc. on RHEL 6 or later. Personally I think for good reasons. And for what it's worth, you get Oracle Linux for free, including the latest patches without the need for a subscription (http://public-yum.oracle.com). Oracle Linux 6.3 ships with a 3.0 mainstream Linux kernel (UEK2) optimized for Oracle. It provides the "oracle-rdbms-server-11gr2-preinstall" rpm package that does all the prerequisite setup to install Oracle database, which makes installing Oracle 11g very simple. Having the same vendor for the database and OS is certainly an advantage. I think there is no compelling reason not to switch to Oracle Linux, in particular if you intend to use it for any Oracle products, unless you want to shoot yourself in the foot now or later.