I absolutely agree that ranting to oneself is abusive when it's not really to oneself! Some people who rant like this absolutely do it intentionally within earshot of their victims, in order to frighten them. Other people who do it are careful about keeping it away from people they care about, because it is absolutely not intended for consumption by other humans.

Given that after 16 years this is something new she just learned her spouse does, EITHER it is ACTUALLY brand-new behavior (and therefore extremely concerning) or it's something he's always done (to which she was unfortunately exposed). The things she should do in response are pretty different depending on which it was, imho.