A long time ago when I was doing my engineering degree, we were taught the basics of piston design with dissimilar metals. The clearances needed to be specified so that you didn't have blow-by at operating temperatures (and also not excessive gaps in the bearings) but this then resulted in small and potentially negative clearances at low temperatures. We had to specify a 'do not move below' temperature that ensured no combination of manufacturing tolerances would result in a nil or negative clearance. I don't recall ever having an issue specifying a suitable multiple-grade oil, but we always had issues with clearances at low temperaures.
I would be astounded if the manufacturer recommendation is based on anything other than metal to metal clearances (as they already specify oils for different temperatures and probably don't care if a cold soaked battery doesn't have the oomph to crank a cold piston engine to light). Grinding metal to metal that is impossible to lube due to no clearance will definitely be a problem they would reasonably be expected to tell customers to avoid!