You might mention to him that an injured Hog can and will come right after you. The Sows often come in head back about crotch high. The Boars slash at your legs and can make some nasty gashes.
What he wants and what is safe and practical may not be the same.
Tell him to test whatever bullet he decides on, not every pistol will reliable feed certain bullet shapes. If he has to use the 9 my advice would be to not stop shooting until the Hog stops wiggling. Which is going to tear up some meat.