Assuming alloy spacers, in the same way alloy wheels can 'bond' themselves to the hubs I would smear a coating on the spacers too to prevent any issues when you need to remove the wheels in the future etc.
Make sure they are hubcentric spacers ie they have a lip that sits inside the hub ( same as the wheel centre would do) - otherwise the wheel studs have to take all the stress and they are not designed for that weight . And no need for copper/grease.
Hub centric spacers that bolt on so no need for longer bolts. I've fitted the wheels but don't like them enough to refurb them and fit new tyres (16" MB Alamak Alloys) So I'll refit my 17" Intra wheels with a set of new tyres.