I've replaced evaporator fans before, but on Whirlpool/Coldspots. It's probably not a big deal to get at it on your GE (presuming the drawer can be easily removed for access), but finding a fan that's an exact fit might be a challenge. If only the motor is bad, you may be able to re-use the existing mounting brackets for a new motor (with similar specs) or find a universal fit replacement assembly and be back in business without hitting a bunch of snags.
On our '70 Whirlpool top-mount, even though the fan was running slowly, it managed to keep things cool. My experience told me that the air movement should have been stronger, so I finally took the time to install a new fan. What a difference! I have to assume it increased efficiency, or at the very least provided more even temperature distribution throughout the fridge and freezer sections.