A small amount of Oreos should not cause any immediate health issues to dogs, but it does not mean they are healthy for them. Oreos are high in sugar and fats. They also contain cocoa, which may induce toxicosis in dogs due to its theobromine content when consumed in large quantities.
Risks
Oreos contain cocoa powder which is toxic for dogs. Although Oreo's cocoa content is low and will unlikely cause any immediate harm, Oreos are not a healthy snack for dogs.
Oreos are high in sugar and fat that can cause diabetes, tooth decay, and obesity in dogs if consumed excessively for the long term.