Maybe it's also just worth to write a quick blog post showing how to drive index updates through Oracle data change notifications

I don't think that will be very simple to write a "quick blog", the trigger will fire in the context of SQL relational tables but we expect mapped objects, and denormalized structures.. even triggers from "containedIn" relations with some specific depth of recursion.
The code living in the database would need to depend on Hibernate ORM and Hibernate Search?