Vampiric Bite. Your fanged bite is a natural weapon, which counts as a simple melee weapon with which you are proficient.
Moonk Weapons: At 1st level, your practice of martial arts gives you mastery of combat styles that use unarmed strikes and monk weapons, which are shortswords and any simple melee weapons that don't have the two-handed or heavy property.
I read this as yes, so the Vampiric bite would scale as a Monk weapon and would use Dexterity instead of Constitution.
Moonk Weapons: At 1st level, your practice of martial arts gives you mastery of combat styles that use unarmed strikes and monk weapons, which are shortswords and any simple melee weapons that don't have the two-handed or heavy property.
I read this as yes, so the Vampiric bite would scale as a Monk weapon and would use Dexterity instead of Constitution.