To my knowledge OpenFTS does not support Oracle yet, whereas Intermedia (obviously) does not support Postgres. I assume you talk about the Oracle version of OpenACS and the site-wide-search module should be able to access Intermedia INSO features. A documentation on how the Content Repository makes use of Intermedia can be found at
https://openacs.org/doc/acs-content-repository/guide/search.html.
