I know if you are going to use silencers you should tune with them on your bow. But silencers aren't used as a tuning factor or tuning instrument. If they are, there's something else wrong with the set up.
Also, if your hunt/shot comes down to what silencer you have on your bow when its raining, that would make for a poor excuse for a miss don't you think?
Do you really think with every bit of your equipment and yourself being totally wet that your silencers are the only blame?
Just something to think about.