Are you possibly talking about the plastic spacers that Shimano uses to make the difference between 68mm and 73mm bottom-bracket shells?

FWIW, I just installed an SLX crankset, including the bottom-bracket that came with it. I don't recall how many of the spacers I used at the moment -- I used what the instructions said to use for my width of shell -- but I can tell you that there is no washer of any sort between either crank arm and external bearing cup.