In essence SELinux is a set of kernel modifications and user-space tools that have been added to various Linux distributions. Its architecture strives to separate enforcement of security decisions from the security policy itself and streamlines the volume of software charged with security policy enforcement. This will help you to harden your system and enforce more strict security rules.
Generally speaking the implementation of SELinux on your Oracle Linux installations is a good idea and will help you to raise your level of security. Issue with SELinux is that it is a not well understood solution which is often seen as a hinder rather then an addition to your system. To Promote SELinux and to provide more information Oracle has released the below video which can help you to understand SELinux in more detail and to help you understand why this should be included in your archtecture for systems that are responsible for critical business processes and/or old critical and confidential data.
More on the subject of SELinux can be found on johanlouwers.blogspot.com or the oracle.com website.