The optically labeled dynamic light scattering (DLS) technique was applied to the ternary system containing two stiff polymers, poly(3-(benzyloxycarbonyl)-n-propyl isocyanate) (PBPIC) and poly(n-hexyl isocyanate) (PHIC), and toluene being an isorefractive solvent of PHIC, to measure the tracer diffusion coefficient D-tr,D-P of PBPIC (the probe polymer) in semidilute solutions of PHIC (the matrix polymer). D-tr,D-P is appreciably reduced with increasing the matrix polymer concentration. From the comparison with the theory based on the fuzzy cylinder model, it turns out that the intermolecular hydrodynamic interaction between PBPIC and PHIC chains is more important in the reduction of D-tr,D-P than the entanglement interaction. Comparing the present and previous D-tr,D-P data for various ternary solutions including flexible and/or stiff polymers, we have found that the concentration dependence of D-tr,D-P divided by the infinite-dilution value can be scaled by the overlap concentration of the probe polymer in the unperturbed state, irrespective of the chain stiffness, if the overlap concentration of the matrix polymer is much lower than that of the probe polymer.