Wilwood makes a steel spacer specifically for mounting on their disc brake hub. It's the only spacer I've found that is actually large enough in diameter to fully support the contact ridges on the factor style rims. They designed it to protect their aluminum hub flange.
I had to enlarge the lug holes to allow the spacer to seat flush on the hub flange, as the shoulder of the wheel studs was holding it up from doing just that.
I also installed slightly longer studs to compensate for the thickness the spacer added.
In my case, I have these on the rear wheels for increased tire to leaf spring clearance.