When you say the compressor is on the back, I think what you're referring to is the condenser coils. Those are the ones you want to be concerned about hitting when cutting through the top and are often found inside the exterior skin on most mini-fridges. The compressor is the canister on the bottom.
If the diagram that you linked to is the exact model, then you have everything you need.
It looks to me like you don't have any lines running through the skin, but they are mounted on the back instead.
It should be perfectly safe to put a hole in the top. If you are still concerned about it, start your hole from the inside with a utility knife and cut away the intererior skin, then go slowly through the insulation until you find wires or lines or you can see the inside of the exterior skin.