The only time I apply fades during the mixing stage is when there are intentional fades that certain instruments must have. An example is in the past I have mixed some songs where the music faded out underneath a vocal part that didn't. I of course applied a fade out to the mix, but not the vocal part.
Other than that, a good reason to leave fade out's to the ME is because there is a good chance that he will be increasing the overall volume of the mix, and depending upon how much that is changed, any fade out you applied will sound quite different after the volume increase. This could lead to problems with the fade out sounding "musical".
DO make sure though that you at least mute any tracks that may have noise on them that may show up during the fade out. It is mostly impossible to remove noises the drummer might have made that are on the final mix, or the hiss from a noisy effects processor that isn't supplying any effects during the fade. Make sure those things are silent.
Good luck with your mixes.
Ed