I don't know Japanese but I think correct translation of how Chopper's Rumble Ball works is that it distorts wavelength of DF User's Biochemistry. Rumble is also a continuous resonant deep voice which Oda also used to name Lightning DF,
Combine that with the fact that Oda chose to give Elbaph's God of War also Lightning Powers, his Rival was Nika who had Drums of Liberation. Chopper's Home is called Drum Island, these Ancient Gods having some kind of soundwaves that affect their surroundings, and the current focus on Brook & Music in general ... etc We also know that Observation Haki is also called Mantra, what does that mean? A mantra is a sacred sound, syllable, word or phrase repeated during meditation or prayer to aid concentration, foster spiritual growth or create positive vibrations.
Imo It's all about sound & vibrations, Chopper's Monster Point Form which uses Rumble Ball is probably making his body create a distortion signal in Imu's Victims bodies which makes them disconnect from his control, forcing those shadows to leave their bodies,
Also, this theory is very convenient because many people wondered how can SHs pose a threat to WG if only their Top 2 or Top 3 have CoC?
If vibrations/sound/audio waves can be a solution, then all SHs have access to them, why do you think Oda taught Robin Fish-Men Karate?
Jinbe already has it too, Brook have hypnotic music, Usopp & Nami can apply Dials to their weapons & Franky is a Cyborg, He can get whatever He needs,
Now think what could someone with DF to literally produce & control unlimited amounts of vibrations do with such knowledge?