Yes it is possible, providing the tank is heavily planted and well maintained. I've used an Eheim skimmer before on its own in a nano with the top section removed and the top of the filter sponge exposed just at water level.
Advantages are, it brings the outlet nearer the surface so there is good surface water movement, it's shrimp safe, and provides more room for a nano heater beneath and hardscape and plants, especially in a shallow aquarium. I think I've seen something similar at AG on a few of their nano tanks too.