As I understand it from previous posts, the background exercisers in Cathe videos are her long time friends. I think they are also instructors of some sort (Rhonda is an instructor, Cedie is a PE instructor). I think because of a lot of dedication involved in filming (hours of practicing), she prefers to select people she knows who can do the job well. And they know that what she expects from them. I think Cathe videos come close to perfection... the set is beautiful, she cues well, great outfit, great-looking (ripped) exercisers, and they hardly made a mistake (though I have caught some little ones... which makes us all human!).
As for viewing the filming, I don't know. Offer her enough money, may be she caved in...