as long as you are using the collet that comes with your motor and has the same diameter as the inner on the bearing it is fine not to use a washer.
The collet closes up and only pushes on the inner of the bearing just like a washer. using a washer doesn't spread the load out when tightening the flywheel on beacause you are only pushing on the bearing inner anyway...
I have confirmed this with boca also and mugen...
The washer as mentioned is only for spacing out the flywheel from the crank case.