By "approach aid," I assume you mean as an approved instrument approach procedure. GPS approaches are the best thing since sliced bread...such approaches are widely used in the U.S. And precision approaches are now being published... The technology is very mature and impressive in its capabilities.
The FAA's Aeronautical Information Manual (AIM) has some very good discussion on GPS approaches. There's an additional section that specifically addresses Helicopter Only GPS approaches. Google will point you in the right direction...
Good luck!