The crab steer would be the same type of setup you would find on a rock buggy except instead of offering funky traction vectoring it is used to provide the truck with near zero turn radii. Moving slowing it will pivot about center thus avoiding dragging the attachment through deep snow or having to pull of a turn that looks like a spirograph drawing.
From the pictures on the auction, it looks like the front overhang and rear overhang are almost equal with respect to the axle center lines.
The system is probably a complete front steer axle with the PS gear plumbed backwards so the rear steers opposite. I can't see too much need to steer in sympathy on a working truck versus a buggy.