The reorientation of spin probes with very different aspect ratios, dissolved in a polymeric liquid crystal, is studied by non-linear Electron Spin Resonance. A scaling law between the rotational correlation time tau and the macroscopic viscosity, as measured via the dynamic shift factor a(T), is found. A discussion on the current interpretations of the scaling, which takes the form tau proportional to a(T)(xi) with 0 less than or equal to xi less than or equal to 1, is given.