Yes. Many, many people (including me) don't speak up when we see someone else doing something wrong. These ethics courses not only drill home the point of the importance of speaking up, but helpfully give many mechanisms in which one can speak up anonymously, or otherwise in a protected manner.

A hypothetical of a situation the GP may have had in mind would be a person who is thinking of fudging or taking a shortcut, but doesn't want anything bad to happen. Ethics courses can show how minor deviations in ethical practice can have major impacts (jokingly - https://www.youtube.com/watch?v=1dWjKkF0Zi4 ). These courses can also show that actively stopping work for an ethical reason will not be punished or looked down on in any way. Because of this the person will feel confident in checking their initial impulse to fudge and instead do what's right.

Showing people how they can be ethical is just as important as showing them what ethics are. We don't need to be moral heroes in order to take more ethical action.