Your advice from legal is conservative, but arguably in the wrong direction.
Under Texas law, yelling "I'm going to kill everyone here and then kill myself" constitutes what is termed a terrorist threat. It's called different things in different states but, typically, that's a crime. You do not have to accomodate criminal behavior. That's like saying a person afflicted with psychopathy and sociopathy can only be reprimanded when they actually kill people because they can't help their abnormal urges, given that those afflictions are deemed to significantly affect one or more life functions by legal counsel.
I would, literally, fire our lawyer if he said that to me in a case like that. You are bound under OSHA to provide a safe work site. You have an employee that has threatened your other employees and who is known to have episodes during which he cannot control his temper. Which takes precedence, OSHA or ADA? Are we clear that ADA even applies? I don't think your lawyer gave it much thought. Time to get a new lawyer in my opinion. It's not as simple as saying you can't do anything because he "may have a disability".
My wife has a lot of ADA experience and she said that life is easy when you have EAP. If you want to take the most conservative route, then you force mandatory EAP with pay and refuse to allow the employee to return to work until a psychiatrist (not a psychologist) says that the person is not a threat to himself or his co-workers. This strategy accomplishes several things. 1) It takes the Company out of the decision making loop, meaning that whatever decision is made, is not due to any illegal discriminatory animus on the part of the company. 2) Because the person is paid, they cannot say that they've suffered any harm so there is no cause of action. 3) If the person turns out not to be safe around their co-workers, that call was made by a medical practitioner and not the Company, again putting liability in someone else's house. She agrees that each case is different, each circuit is different, and whether OSHA trumps ADA or the other way around is not always clear but that mandatory EAP with pay makes all the problems go away.