The high emissivity material will radiate heat more effectively, and therefore run cooler than the low emissivity material. The steady state temperature for both will be different at the same input power.
That seems impossible. It would allow a perpetual motion machine. In any case, the steady state terminal air temperature in a flow calorimeter for any given power level must be the same, or the energy is either disappearing into the void, or appearing out of nowhere. With a flow calorimeter, when a body produces a given power level such as 100 W, the Delta T air temperature is always the same. With Mizuno's reactor, the duct is 66 mm, the air flow rate is 3.957 m/s, so the calibration constant is 0.0552 K/W. So, 100 W produces a 5.52 deg C Delta T. It makes no difference what color the sample is, what the emissivity is, or whether the sample is so small it is incandescent or so large you can touch it with your hand. None of that matters. The calorimeter cannot distinguish between those states. It always produces a 5.52 deg C temperature difference. The equation couldn't be simpler:
Energy (kJ/s) = Mass of air (kg/s) * Heat capacity of air (kJ/kg) * Temp difference (K)