Can I use Make to build integrations to my own Oracle DB?

Where Make doesn’t (yet) have a specific app, you can always use the HTTP app to send a suitable request to a REST API endpoint.

Oracle Apex has a REST API. But of course that’s different from talking directly to the underlying Oracle database.

There is a REST-Enabled SQL service (search Google for details) for the underlying Oracle RDBMS that can be used to send SQL statements by an HTTP POST request.