I recommend insisting upon a legal evaluation of his state, which shouldn't be a problem if you have shared custody. Drug use could also be related to how he behaves, so make sure to insist on testing that as well.
I come from a family where there has been schizophrenia present, and my current boyfriend's mother has schizophrenia too. From what you have told me, his symptoms could math the messy period before the "acute" psychosis stage of schizophrenia.
However, there are other mental disorders besides schizophrenia, and the behavior could be related to something entirely else as well. Without a proper psychological evaluation it's impossible to make any diagnosis, and I fully support searching professional help.
Even if he is schizophrenic, it doesn't mean that he is automatically a danger to your son as there are plenty of peaceful schizophrenics out there. The acute stage of the disorder might make him very unpredictable though, and will definitely cause your son to be scared of him. If he is schizophrenic, getting him on proper meds is essential, so no matter if he is dangerous or not, getting him to a doctor is important.