The genset is probably real sine wave AC, but the frequency is probably a bit off. I have a 12.5 kW diesel out back, when I bring it up my APC UPSs don't care for it unless it's within 1/2 (.5) cycles of 60 Hz, my genset holds between 60 and 61 Hz, as it gets above about 60.5 the UPSs get angry.

Bill