If you are looking to integrate w ES, the ossec_file_integrity_monitoring source type maps to change analysis and the ossec_alert maps to alert data model.
You could adapt some of the existing correlation searches that use change analysis to fit this need or use the guided search to build a correlation search. You will want to think about how often you want to be alerted to these changes and if there is a certain threshold you would want to set.
Yes. You can use the common information model and and the associated TA on splunkbase https://splunkbase.splunk.com/app/2808/ and build a datamodel search using the change analysis data model or you can just take the ossec data in and then build some searches based on what you see.