Is the partner of a no trump opener also the team "captain" on defense?
This is nonsensical reasoning.

In any sort of team game you would be frequently doubling the opponents in to game (minus 530 or 730) for a long shot at a doubled set (of plus 100 or 200). To make matters worse, the double will just refine the ability of declarer to place defensive cards properly, which is already tuned by the 1NT opening. This is simply losing bridge.  Even at match-points, white against red, I cannot conceive of a game situation where I am not better off to try and get a plus by defending better than the field.

Further, captaincy in defense is a separate concern than in bidding. In defense, the captain is the partner who first figures how to maximize defensive tricks, and is most often the defender with the most points. Captain, once that is known, is entitled to lie with defensive signals while non-captain should only make mandatory false cards and otherwise signal honestly.