Pickup trucks have 15" wheels and tires. 1 ton and larger trucks have 20" tires and wheels that have a different offset (think dually wheels compared to single wheels) then the pickup wheels. The rear portion of the big truck fenders are also longer then the rear portion of the pickup fenders. Big trucks sit higher off the ground and the running boards attach to the bottom edge of the fenders. The fenders are longer, so the running boards could be lower, to enable easier truck entry.

You can use the big truck fenders as they are, but the are wider and have 4"-5" larger wheel openings then the pickup fenders and might look a bit strange with the smaller Dakota wheels. Then the rear portion of the fenders will probably be sitting on the ground (without even lowering the truck).

Wouldn't have to worry about any tire rub issues with the big truck fenders though.
Gene