First I assume you are using Oracle DataServer from Progress.
If that is the case, bear in mind that all USE-INDEX will be translated basically into ORDER BY in the resulting query, so mostly being used to order not to access the data.
If you want a know how your information is accessed you'll need to enable qt_debug when connecting to the schema holder, that will allow you to print many information about how your progress code is translated to SQL to access the Oracle DB. You'll need to analyze those SQL (SQL EXPLAIN as an example) to see the performance of your queries and how they are accessing the DB.