The rule of thumb for Object Resistance is you roll that if the spell targeting a nonliving object invokes a resistance test that's unavailable to that nonliving object.
Ergo, (most) direct combat spells invoke Body as the resistance dice pool, and vehicles/drones have that so that's what you roll. Those direct combat spells that invoke Willpower will also be Mana type spells, which can't target non-living things anyway. But technically, if there were a direct combat spell that's Physical in nature and involves Willpower as its resistance, then yes Object Resistance would apply for vehicles/drones because they lack Willpower.
Indirect combat spells work just like physical attacks, at least when it comes to resolving whether or not they hit. Since that's covered as well, there's no Object Resistance to fall back on here, either.
