I ran WMO (filtered to 10 micron via hydraulic oil filters) in my 6.5L. At 40% WMO, the optical eye in the electronic IP would be confused on startup, resulting in crappy running until I re-keyed the truck. Never had the problem on lower concentrations, so I would dump 5 gal WMO in at a 30 gal fill. Saved me money in the long run, and didn't anger the truck.
I would think that the mechanical IP in a 6.2L would be more tolerant to higher levels than my 6.5L was...
That said, I was led to believe that the DB2 pump has a rather small drive shaft, and thick oil (IE, cold WMO) could snap the shaft. A bud with a Cummins 4BT (simmilar to DB2 pump as I understand it) in his chev had his shaft snap running straight hydraulic oil (10wt) on a 30 degree morning. Given how much WMO thins out with even low amounts of gas or diesel, I should think that cutting it even just 10 to 20% should be fine in warmer climates.
Oh, and I make it a point not to ever run used diesel oil in my trucks. All that soot can NOT be good for the injectors, pump, etc... It also tends to clog filters faster I believe... Not to mention usually being thicker.
Chris