The UEK kernel is maintained by Oracle and designed and tested for OL 5 and OL 6. The UEK kernel aims to provides a modern kernel and is optimized for Oracle products. The Oracle UEK kernel is fully user-space compatible with RHEL and applications that are certified for RHEL do not need to be re-certified for Oracle Linux. The current UEK Release 2 kernel version 2.6.39 is based on the 3.0.36 stable upstream kernel.
The UEK kernel version alone cannot be used to determine your Oracle Linux Release version. The following document will explain how to determine your Oracle Linux Release version: http://www.oracle.com/us/technologies/027626.pdf
You should always use the YUM utility to upgrade any software, including the kernel. It will automatically resolve installation dependencies and abort on software conflicts.