It's very unlikely that front squats would work the lower traps to any significant degree.
The lower fibres of the trapezius are responsible for the following movements of the scapula1:
Upper rotation (in which the lowest point of the shoulder blade moves laterally and upward)
Adduction (in which the shoulder blades pull together)
Depression (in which the ...
You're right. Here is why:
Lower traps help depress shoulder blades and well as shoulder upward rotation and external rotation. Retracting your shoulders and pulling your shoulders down activates your lower traps the same way a shrug activates upper traps. For this reason, reverse shrugs which you can do on a cable machine work lower traps. To get maximal ...