Three distinct Subaru's here: the WRX STi for the Japanese Rally Championship, the WRX STi for Global Rallycross and lastly the custom SuperGT support Outback.
The Japanese rally spec appears purest and most like the production car, aside from chassis bracing for the roll cage, a roof vent for the drivers to get some air, and a slightly taller ride height on rally-sped wheels and tires.
The Global Rallycross car is interesting: it wears a much wider front-end and bumper that acts as a bit of a flexible splitter. This seems able to take impacts and also be a decent aero helper. The side sills below the doors are much wider, likely for functional reasons to keep the rocks from shooting up toward any glass.
The most intriguing element of the rallycross car are the vertical vanes inside the rear wing. These recall Ken Block's Subaru's, and these vanes are likely there for a dual purpose: snap-straight assistance when sliding sideways, helping come out of any big drifts cleanly. Secondly, the snap-straight functionality is also useful for a safety reason. This tech is used in NASCAR, LeMans and elsewhere to help a crashing car impact head-on.
Frontal crashes are safer for drivers than hitting the wall sideways, as the racecars still have much of the production models' crash structure in front. Alternatively, there are very few ways to make a high-speed side collision safe; there just isn't enough crush space in the doors -- which generally lack side-impact beams of road cars.