That is actually a common way to unload gondolas. I've seen videos of wheeled end loaders/excavators climbing up without using ramps, just the bucket. Lift the end next to the car by putting the bucket on the end of the car, pull the tractor close enough to get the first axle on the car, then use the excavator arm to lift and push the other end. I've never seen a tracked excavator do it, but it's basically the same trick, except that they have to turn the cab and boom.
Some tractors now come with guides to keep the wheels on top of the car sides, so the driver doesn't have to steer as carefully.
