Hauling HAZMAT in a cargo van, in and of itself, isn't enough to make you have to enter the scales. It must be a placardable amount, which, generally means, anything that is placardable only in amounts of 1001 pound or more. This includes paint, solvents, batteries, most all Class 9 cargo, etc.
A 55 gallon drum of HAZMAT paint is going to weigh in at around 750 pounds, give or take. You have to have a HAZMAT endorsement to haul it, but it's not a placardable amount, and therefor does not require you to log or scale.
HAZMAT that is placardable in any amount, even one pound, with few exceptions, cannot even be carried in a van. This includes inhalation hazards, oxidizers, explosives, most poisons, etc.
Even if, for some reason, you choose to not obtain a HAZMAT endorsement for your CDL, I highly recommend studying the HAZMAT sections of the CDL handbook. You'll be more aware, and more informed, about the vehicles that are all around you out here. Same holds true for the CDL sections if you just have a regular operator's license.
Personally, I think that every driver of any motor vehicle should have to take the CDL test, even if all they ever drive is a Camry or the Soccer Mommy Van.
Slow and steady, even in expediting, wins the race - Aesop