We determine experimentally the "dilution exponent" alpha for entangled polymers from the scaling of terminal crossover frequency with entanglement density from the linear rheology of three 1,4-polybutadiene star polymers that are blended with low-molecular-weight, unentangled linear 1,4-polybutadiene at various star volume fractions, phi(s). Assuming that the rheology of monodisperse stars depends solely on the plateau modulus G(N)(phi(s)) proportional to phi(1+alpha)(s), the number of entanglements per chain M-e(phi(s)) proportional to phi(-alpha)(s), and the tube-segment frictional Rouse time tau(e)(phi(s)) proportional to phi(-2 alpha)(s), we show that only an alpha = 1 scaling superposes the M-e(phi(s)) dependence of the terminal crossover frequency omega(x,t) of the blends with those of pure stars, not alpha = 4/3. This is the first determination of a for star polymers that does not rely on any particular tube model implementation. We also show that a generalized tube model, the "Hierarchical model", using the "Das" parameter set with alpha = 1 reasonably predicts the rheological data of the melts and blends featured in this paper.