Hi, Spadone,
I hope you are not one of those people who do something just to defy conventional ideas, and to hell with anything else. The fact that you are even concerned about humaneness indicates you are not, so why go that route? The 9mm is not suitable for deer over 50 feet, for several reasons aside from legality.
If you are a stalker who can approach within a few feet of a deer and take a clean head shot, maybe. If not, leave the 9mm at home and use a more suitable cartridge.
Jim