In the simulator I have trained recovery from just about any upset possible with a 737. The upset is generally set up by one pilot while the other has his eyes closed. Great training!
What is very difficult to simulate is the startle effect or the confusion of an unexpected upset. A nose down, high thrust, trimmed down situation at low altitude is difficult but possible to save if you take the correct action right away. If you are condused and need to analyze the situation for a few seconds, you are dead.