I don't particularly care for them but my mother-in-law lost about 50 lbs eating just the Weight Watchers meals over a six month period. I think she is just eating healthy foods that cooks herself to maintain.
I say that you could lose weight doing that, but I think it would be quite unhealthy as there will be little variety in your diet, try adding fruit and veg and light, healthy snacks during the day.
Yes, you can lose weight by including a frozen meal in your day as long as you're adhering to your SmartPoints and remaining within the restrictions of your diet with increased physical activity.