Like at the OK Sugar Art show
Absolutely. You wouldn't believe the time it takes to decorate one of those. My fondant is hard as a rock when I'm all done with one. Well, the huge show cake I did a few months ago is definitely a rock now!
Yes, most of the show cakes are styrofoam dummies.
If a portion of the cake must be carved to get a shape, then it must be made from real cake. Several photos of the carving in process must provided, as well.
Yep most all are dummies. The exception is if it is something "odd" - you have to "prove" that it can be done in cake. (like the star shaped cake at OSAS a couple of years ago)
Often the rules state the cake is to be a dummy, but the concept must be able to be executed in real cake. As well, many of the same rules apply to the dummies such as no wires placed into the cake, etc.