The gun will be louder with super sonic ammo. That's all. Some countries require suppressors for big game hunting. I guarantee they're not using subsonic ammo. Muzzle blast is a HUGE part of the noise, much worse than the sonic boom of the bullet. Hunting with a suppressor is not primarily about not scaring game, it's about "noise pollution".
If your intent is to try not to spook game, subsonic ammo might be necessary but that's the only reason.