The scientific answer is "yes". Every single drop of electricity you use in the car decreases your overall mpg. By using the radio, you're drawing amp-hours out of the 12V battery, which gets charged by the DC-DC converter, which gets energized by the main 144V battery pack, which gets charged by the 10kW electric engine, which gets energized by the ICE, which is powered by gasoline.
The practical answer is "no". The amount of energy required to power the Honda-installed radio is trivial. The difference in fuel economy would get lost-in-the-noise of other much more contributing factors (weather conditions, tire pressure, driving habits, etc).
I have a couple of 1+ mile FAS coasts to work. With the headlights on and radio with 150 watt amp, the Optima Yellow Top starts at 12.5v and drops .1v every 8 to 10 seconds. Lights on and no stereo/amp it drops .1v every 24 seconds. Yes, stereo with amp does pull considerably.