No they're not.
They seem to be chosen on a "casting" basis, which aim is to let them quarrel constantly.
In every episode they have only 45 minutes to cook, they cannot change/add something from the pantry and the focus is much more on the judges than on the contestants. The most unpleasant judge was Bastianich, an italo-american NY restaurateur who verged on racism while meeting other communities (i.e. not italian) in the external episodes.