The drum-shaped worm grinding wheel, a specialized cutting tool used in face gear worm grinding, is typically shaped by a conjugate-involute dressing wheel. The accuracy of the dressing wheel profile significantly influences the precision of the worm grinding wheel and, consequently, the machining accuracy of the face gear. Despite its critical role, existing international and national standards primarily address cylindrical dressing wheels, rendering them unsuitable for involute dressing wheels. As a result, the accuracy of involute dressing wheels is often assessed indirectly through the profiles of machined products, an approach that lacks precision. Additionally, the dressing process of the drum-shaped worm grinding wheel involves complex movements, and the impact of geometric errors in the dressing wheel on the final grinding wheel profile remains inadequately understood. This study addresses these challenges by proposing evaluation criteria—tooth profile deviation and symmetry deviation—to quantify the profile accuracy of involute dressing wheels. A mathematical model is developed by analyzing the relative motion between the dressing wheel and the worm grinding wheel during the dressing process, establishing a clear error mapping relationship. The proposed model is validated through a series of dressing experiments, demonstrating its effectiveness in accurately assessing the profile accuracy of involute dressing wheels.