Obviously the quarterback in the huddle doesn't have to play QB.
But I'm almost certain that someone who is listed on the roster as a quarterback must be in on the field for each offensive play. So the #1 QB or #2 QB must be on the field... or #3 QB, but you get into all that emergency QB stuff with that.
I'm not sure about the numbers thing... it doens't quite make sense to me considering WR's now regularly wear numbers 10 through 19, which are all QB numbers.