No, the wheel bolts do not hold the weight.
Come on Rich... think about it... they provide clamping force to hold the wheel mounting face to the face of the hub... each bolt can give many tonnes of clamping force..
The hubcentric spacers and what not are there to provide a) easier mounting of the wheel and b.) provide some reduction in vibration, due to wheels which are not centrally mounted, which can then cause wheel bolts to come loose.