_array1 is a list of vehicles, not a vehicle itself. Thus, you need to iterate through it, then iterate through the crew using two separate forEach loops.
There isn't a class called "vehicle", instead use "AllVehicles" (which includes infantry). Remember also that men on foot have a single crewman (that is, themselves!).
_array1 = [_xx,_yy,0] nearObjects ["AllVehicles", (100 + _seek)]
{ { _x setDammage 1} forEach (crew _x) } forEach _array1;