There's usually no CAA examiner involved - for want of a better description the CAA devolve the authority to do all the Command training and checking to the airline's training department ( in my outfit's case). I guess, in theory, you could end up with a CAA examiner "checking the checker", either by sitting in on the Simulator Command Check or sitting in on the final Route Check.....
That would do wonders for the candidates nerves.....
As to the point about who sits where? - UK rules are,as far as I'm aware, that the Commander must be at the controls for the take-off and landing - perhaps the Commander on jumpseat is a non-UK thing?