We have an Oracle test server sending plain text audit logs via syslog to Splunk, and though we have the InfoSec and Splunk Add-On for Oracle Database add-ons installed, the logs are not getting the appropriate CIM-compliant sourcetypes added to them so they're not showing up as expected in the authentications area of the IS dashboards and searches. We decided to go with plain text audit logs as we didn't need the inventory and performance events, so opted against using DB Connect. Using a forwarder is not out of the question, we just chose syslog since it meant not having to install anything on the Oracle server.
I've been reading the documentation and it seems unclear whether the Splunk Add-On for Oracle Database add-on must be installed on indexers in addition to the search head in order for the sourcetypes, tags, etc to get added like I thought they would. The documentation says it's conditional: "Required if you are monitoring files locally on Oracle servers with universal forwarders."
Since we're not using a forwarder, perhaps I just missed something in the configuration of the add-on? As far as I can tell all the apps and their pre-reqs are configured and enabled.
Edited for additional info: Splunk 7, Splunk Add-on for Oracle v3.7.0, and it appears we have one search head and two indexers.