At this point you'd be hard pressed to find any fuel/oil supplier that uses anything other then ulsd for heating, off or on road diesel. Sulfur content was really the only thing separating them to begin with, heating oil traditionally was 4k ppm sulfur content same as off road diesel. With the advent of interim tier 4 and tier 4 engines, pretty much everyone was forced to switch to ulsd. We had loads of wrong fuel issues with generators and off road engines, everywhere till the fuel suppliers got their act together. Basically came down to being easier for the suppliers to stock ulsd for all uses vs finding out if it's going to be used in an engine or for heating, and depending on the customer not to use heating oil in their tractor, truck, etc.
Only difference at this point is if it has die or not, or if it's taxed or not.
There was some legislation pertaining to heating oil back around 2012, possibly as late as 2015 for sulfur levels, but I never followed along to see if it ever took effect or came to more then north estern usa.