We use electron paramagnetic resonance (EPR) spectroscopy and photo-induced EPR to discern the compensating species associated with the Fermi level extracted from temperature-dependent Hall measurements of vanadium-doped 4H SiC and high purity semi-insulating 4H SiC. The results demonstrate that the V4+/V5+ transition is responsible for the 1.6 eV carrier activation energy (E-a) measured in some of the vanadium-doped samples. In other vanadium-doped wafers, photo-EPR data reveal transitions for V3+ at energies between 1.1 and 1.25 eV, consistent with the activation energy. However, the relationship between V3+ and E-a is not clear. The carbon vacancy (VC), which is detected in all HPSI wafers, exhibits a range of photo-thresholds similar to the varying values measured for E-a. Therefore, although EPR measurements show that the number of uncompensated carbon vacancies is below that thought necessary to neutralize the residual shallow donors and acceptors, V-C likely participates in compensation.