Polys and oscars work well together.
If you follow some simple advice. Neither one can be considerably larger than the other. If one has to be bigger, make it the poly.
I've kept senegals, my ornate, lapredei, delhezi, and palmas pollis with oscars with no issues at any time.
I followed the same advice I give today and was glad I did so. Either species can eat or bully the other one to death depending on their temperament given a large size difference. Some fish are just mellow, and well, others are not.
I also suggest sticking with either some senegals, delhezis, or an ornate for your oscar. Get larger polys than your oscar. IME polys typically don't grow as fast as oscars do. Polys are funny in that regard, some grow really fast, and others grow very slowly. My first delhezi went from 4" to 7" in 6 months, my two delhezi I'm growing out and got a 4" are now only 5" after 6 months. At this rate they will go to the poly tank in another 6 months or so.