Rules for parked cars
 

Legally speaking, if a person is parked illegally and their car is hit by a person, say a delivery van, is there any way that 100 percent fault wouldn't fall on the delivery van?

Case in point - The back alley behind my business is frequently traveled and people due to the snow have parked in non parking zones impeding traffic. If one of these vehicles were hit, who would be at fault?

Berz out.

The driver of the delivery van would be at fault

Agreed. They might get a ticket for illegal parking, but the van driver is still the one in control of the moving vehicle.