You need to check the AP placement table at your son’s school to see how they award credit.
Since both AP Physic 1 and AP physics 2 cover the same material – an entire year of college level algebra-based physics–and usually both give credit for an entire year of college physics at most colleges, I don’t think it will make any difference whether he sends the AP Phys 2 score or not. He likely won’t get additional physics credits and he will still need to supplement his physics coursework for a number of medical schools.