What do you mean specifically by integration with Joomla? Would it be using Splunk to help monitor/search Joomla log files for issues or something else? There is not a specific Joomla app on Splunkbase currently that I could see.
We do provide REST APIs and SDKs for you to create our own views and integrate with other solutions. Look at some of the examples here in the Application gallery. http://dev.splunk.com/view/SP-CAAADQ8