The VP machine deals from a 52 card deck (on JOB machines). Discards are not put back into the deck for the draw.

However, whether the draw cards are preselected or determined only when you hit the Draw button is immaterial. The odds and optimum playing strategy would be the same either way. If you had a way to sync your Draw with the RNG, maybe you could affect the cards drawn, but obviously you can't. The RNG runs very fast and being isolated from the machine's circuitry, you have no way to time things. Players sometimes like to think they can, as it give them the feeling of having more control over the game.