No he doesn't. The Come player can press his finger on his monitor for the midnight horn bet just as easily the don't side bettor Alan (assuming the team even wants to decrease their EV by placing a horn bet on the Bar) - you just need to designate one team member to do it. Furthermore your statement "The Don't player needs to bet the 12 to protect his bet" is incorrect as I posted previously. Nothing is mentioned about a team in this statement.