I think the issue is the sulfur content of the fuel, not whether it's off-road or on-road. People always mix this up and equate the two where they shouldn't.
Off-road just means there is no highway tax in the fuel price, and the fuel is dyed red to indicate that. This is not a reliable indicator of sulfur content.
On-road diesel MUST be 15 PPM or less sulfur, otherwise known as ULSD (Ultra low Sulfur Diesel), so buying on-road assures you are buying ULSD. That relationship is reliable, i.e. on-road = Highway taxes = no red dye = ULSD
Off-road is not REQUIRED to be ULSD, but in practice it almost always is. Just ask the fuel distributor/dealer to confirm. So off-road = no highway taxes = red dye = (ULSD or LSD). In other words, it might be ULSD, but it's not guaranteed - you need to ask/check.
I just had my 250 gal storage tank filled the other day and it says right on the slip that it's off-road ULSD. Good thing because my excavator requires ULSD.