The Hollow position and Hollow Rock are staples for all gymnastics work and gymnasts spend literally hours drilling variations on this movement. To maximise the benefits to your core strength, ensure you build up to a great hollow position before you practise the rocking option.
If you struggle to keep your lower back strongly pressed flat into the ground, then work on progressions, which include deadbugs, hollow hold with bent legs and hands reaching towards feet instead of overhead. As soon as you feel your lower back wanting to lift off the ground, then pull back a little and work the position you are (just) able to keep the core nicely active.