Can hernia cause edema in legs?

Possibly: A femoral hernia could compress on the femoral vein and cause some swelling of the same leg.

Unlikely: A very large ventral hernia (one that hangs down over the thighs), could contribute to leg edema, but associated factors related to obesity and venous stasis disease would probably also be factors. In general, hernias do not cause leg edema unless it is an extreme situation.