welcome to Oscarfishlover
I personally would never try and second-guess an Oscar, they can be very unpredictable so if you value a smaller fish, don't put it in with an Oscar. An Oscar will look on a small fish as food. They may not eat it straight away, it may live in the tank for a long time, however, there is always that risk that the Oscar well eat it. I have myself introduced very small fish in with my Oscars and they have not eaten them, however I wouldn't tell someone else to do the same as me.