Beatmaps must be hit sounded. While every game mode has its own techniques, effective hit sounds in all modes accent the most important parts of the music.
So to answer your question: yes, hitsounds are mandatory. It doesn't have to be very complex though, if you have no idea where to start maybe try adding claps every 2nd/4th beat and a finish on a downbeat every once in a while, then see how it goes.