How do you figure out the str of a Walker vehicle for use of melee weapons?
I believe that this is the answer,
"Attack: This entry indicates an attack the vehicle has, the damage it deals, and the DC to avoid it (if any). Most vehicles have only collision attacks, which deal bludgeoning damage."
If it states the Attack damage, without mentioning add the "+Str Modifier" I think it doesn't add Str to damage.
If you are asking about Wheel Scythes then it tells you there, the vehicle type doesn't change it.
For the purpose of calculating the weapon’s attack, damage, and saving throw modifiers, use the operator’s Strength bonus or +3, whichever is higher.
If you mean the basic 'Collision' attack, then The Artificer is right, there is no strength modifier added to it.