Is bolt tightening torque to be reduced for lubed threads & underhead areas vs. dry?
Yes. How much?
A chart is attached which gives some guidance. As a general matter, a reduction of ~25% seems to be a satisfactory rule of thumb.
For MB 12mm wheel bolts with a dry thread torque range of 80-100 lb-ft., a lubed range of 60-75 lb-ft. would be appropriate.

The remainder of the chart can be viewed via google>Repair Engineering.

Attached Thumbnails