I'm sure the question as to whether the models were premade vs homemade is one that the judges consider when rating each entry, regardless.  If you'll look at last year's winners in the 3d category, the first one with -any- easily recognizable premade Poser figures is the 4th runner up. 

I would guess that amongst the factors of how well made a scene is, how apropos for a holiday card, how creative or humorous it is, that they also look at the effort put into it.  I know that if I see a scene that shows a complex and thought-provoking theme subtly hinted at by the careful configuration of store-bought Poser figures, I would rate it higher in my own personal esteem than a simpler cute card made from scratch.  It's all about how they use the tools they have, not which ones they use.