even tho i haven't had much of a chance to see if it's true or not (no rain). this is what was told to me in the SWM chat when i asked if it helped any with rain-fade. the answer was, "yes, to a small degree the SWM will help with rain fade".
I personally don't see how the SWM could make any difference at all with regard to the amount of signal that is reaching the dish, or the degree of sensitivity in the front end receivers in the LNB assembly. Rain fade does not effect the signal that is sent from the dish to the receiver or multiswitch, and that's where the SWM works.
But I've been proven wrong on more than one occasion, I suppose anything is possible.