Calculations are presented of the effects of nonthermal features on electron cyclotron emission parallel to the magnetic field from energetic electrons in a mirror geometry. The calculations were performed using a one-dimensional radiation transport model with fully relativistic emission and absorption coefficients and generic axial profiles, which allow comparison of the results to a variety of experiments. Where necessary, specific parameters were chosen to be representative of present-day large mirror devices. Primary focus is on the conditions for which the emission is optically thick and the relationship between the radiation temperature (intensity) and the temperature of a primary hot component. It is demonstrated that for many (but not all) conditions the radiation temperature is a useful measure of the hot electron temperature. In particular, dilute super hot tails on the distribution do not adversely affect the radiation temperature to any great degree.