If it's ASTM certified commercial bio-diesel fuel, you shouldn't have a problem, and you'll not likely need a fuel treatment this time of year.

The only Duramax engines that shouldn't use B20+ is the LMM. The higher solvent action of bio can wash cylinder walls during an active Diesel Particulate Filter regeneration. In the LMM, extra fuel is injected into each cylinder during the exhaust stroke, which is then burned in the exhaust system and DPF to oxidize the soot buildup.

The LBZ and earlier engines didn't have DPF regeneration and the latest LML engines use a 9th injector in the exhaust system to inject the extra fuel. GM approves of up to B20 for the LML because of that.