“Scotty and the Secret History of Hollywood” wears a lot of hats, none of which quite fits. A salacious tell-all about the hidden sex lives of postwar movie stars; a peek at the underbelly of the repressive moral dictates of the studio system; a breezy biography of a self-described Hollywood prostitute and procurer; and a psychosexual study of a possibly damaged victim of extreme childhood abuse. Only the last offers a clue to interpreting the movie’s more astonishing revelations and unprobed corners. Until then, Matt Tyrnauer’s gossipy portrait of Scotty Bowers, an impish nonagenarian and ...