Maybe something, maybe nothing. If the dynamo output is loaded, the input motor has to supply all the power that the load draws. If the load draws 5 kw and the system has 85% efficiency, which is about normal, the motor must supply 5884 watts, which is 490.333 amps.
I have tried connecting a 48 v dc motor output shaft with 2.5 kW generator input shaft . surprisingly the generator started and produce electricity . i have also applied 1 kw load at generator