the musicians union has rules about how many notes need to be the same for a melody to be copyrighted.

The style creators never have the same notes as the song for more than a few notes to avoid the rule. That's why the keyboard intros which identify the song always need a little editing to give the original intro.

If the style is very close to the song, they may well have to pay a royalty to the composer/arranger, I don't know. Maybe that is why Yamaha insisted on the removal of their internal styles from the user groups?

thus a style is not the same as a song, but if you can prove creation of an original style you can still sue if someone copies it, or distributes it unauthorised.