REW is fairly tolerant of latency, so it will probably work fine. If there are problems you can make use of the acoustic timing reference option. To do that, select acoustic timing reference in the Analysis preferences. Then open the signal generator, select the measurement sweep, set it for the range you want to measure then save the signal as a WAV, selecting the option to add a timing reference to the signal. Open the measurement dialog, select the option to wait for timing reference then press Measure. Then play the WAV you saves through the system. Note that the settings in the measurement dialog must be exactly the same as those used when saving the WAV, otherwise the result will not be valid.