A statistical approach to the direct calculation of thermal rate constants and cumulative reaction probabilities based on flux correlation functions is presented. It facilitates the accurate treatment of rotational and low frequency vibrational motion in rate constant calculations. Within this approach, a statistical sampling scheme is used to evaluate the trace in the flux correlation function and the multi-configurational time-dependent Hartree (MCTDH) approach is employed to simulate the system dynamics. The OH+Cl-->O+HCl reaction is studied to demonstrate the efficiency of the approach. Known results for vanishing total angular, J=0, are reproduced. Moreover, thermal rate constants are calculated including all internal and rotational degrees of freedom explicitly, i.e., without invoking a J-shifting or K-conserving approximation. Based on these results, the accuracy of the J-shifting approximation is discussed.