It'll be 1 point of non-lethal damage plus poison.
Minimum Damage: If penalties reduce the damage result to less than 1, a hit still deals 1 point of nonlethal damage.
Nothing in the poison rules indicates a non-lethal injury is not an injury.
Bookrat is referring to this:
Minimum Damage
If penalties reduce the damage result to less than 1, a hit still deals 1 point of nonlethal damage.
The scorpion does a puny 1d2 because it's weapon (stinger) is so small. It does -4 damage because it has such a very low STR. End result is the stinger can't really hurt a person very much (1 non-lethal HP that heals by itself in an hour). But, since damage is being done, even though it's non-lethal, the poison will still be applied.
Damage
If your attack succeeds, you deal damage. The type of weapon used determines the amount of damage you deal.Damage reduces a target's current hit points.
Minimum Damage: If penalties reduce the damage result to less than 1, a hit still deals 1 point of nonlethal damage.
Strength Bonus: When you hit with a melee or thrown weapon, including a sling, add your Strength modifier to the damage result. A Strength penalty, but not a bonus, applies on damage rolls made with a bow that is not a composite bow.
Off-Hand Weapon: When you deal damage with a weapon in your off hand, you add only 1/2 your Strength bonus. If you have a Strength penalty, the entire penalty applies.
Wielding a Weapon Two-Handed: When you deal damage with a weapon that you are wielding two-handed, you add 1-1/2 times your Strength bonus (Strength penalties are not multiplied). You don't get this higher Strength bonus, however, when using a light weapon with two hands.
Bolding mine for emphasis but here is what are looking for.
Edit: Stupid ninja tarrasque