I suppose you could consider communicating to the other parents, either through the school or directly, that you are aware of your son’s behavior issues and are working on them and that you support the school taking necessary disciplinary action, and at least reassure them that you are reasonable people who accept responsibility for the behavior problems, and NOT the “how DARE you accuse my precious angel of misbehavior!!?!” type of parents. I was at the receiving end of some bullying in grade school, and because the ringleader bully’s father was a good, reasonable guy, my mom called him directly (rather than deal with the school) and that was the end of that. If he’d been unreasonable/in denial about the bullying, it would have been better to go through the school.
Whether getting in touch with the other parents to apologize/open a line of communication is a good idea depends on whether the other parents are also reasonable, I’d think.