I wish I had the answer. I don't have the cars at my disposal so you could test "draw" when charging - if that is even possible in an EV/EREV. I used to test power draw when the car was off to see if I ha a phantom power draws in my cars that the batteries would seem to die quickly in. Make sure aftermarket items hooked to the accessory fuses were actually turning off, etc...
My guess is that the computers that have to run draw so little power, it probably makes a statistically insignificant amount of difference. A battery warmer/cooler turning on or HVAC pre-conditioning will of course reduce charging rate. Considering in the Volt, running the HVAC in a remote start causes a drain on the battery on 12A, L1 charger.