Some helicopter crashes are caused by a disoriented pilot. This would presumably be impossible with a GPS with terrain maps. Are pilots required to use a GPS when flying a helicopter in the US?
A disoriented pilot may include pilots who are disoriented with respect to attitude. GPS does not provide attitude information, although it could be inferred to a degree.
A Ground Proximity Warning System (GPWS) uses GPS data and digital elevation models (terrain) to predict terrain collisions. Such a device gives warning when an aircraft trajectory is likely to collide or nearly collide with terrain. These systems are common on fixed wing and rotorcraft.
In 2002 the US FAA mandated TAWS or GPWS for all turbine airplanes having 6 or more passengers. I am unaware of a similar requirement for helicopters, but I seldom fly helicopters, particularly larger than a 206.
For helicopter flights there is only a requirement in the US to have maps or charts suitable for the navigation used. If VFR these could be Helicopter charts, terminal charts, sectionals, WAC/ONC, even instrument charts. Old man Jeppesen just made notes on a notebook, and later marketed them.
To specifically answer your question, there are no generalized requirements for GPS or moving map GPS in helicopters.
And as a relevant footnote, GPWS systems have been available at a relatively low cost for general aviation aircraft for well over 20 years, which would provide terrain warning, with verbal audio in the pilot cabin.
No, pilots are not required to use GPS maps or moving GPS while flying helicopters or fixed-wing aircraft.
There are some approaches to landing that require GPS (called RNAV) approaches, but the airports that they serve usually have other types of non-precision approaches as well.
Helicopters have specialized maps that are called Helicopter Route Charts that are supposed to provide additional information relevant to helicopter pilots. These charts may be carried in paper form, although newer aircraft also have them as electronic moving maps. The pilots may also (but are not required to) be using electronic flight bags with moving maps/terrain/synthetic vision.
GPS is never required in any aircraft. No navigational aid/equipment is required in aircraft flying VFR (Visual Flight Rules) or Daytime Special-VFR except for a magnetic compass. Nighttime Special-VFR and all IFR (Instrument Flight Rules) require navigational equipment specific for the flight undertaken and/or the Instrument Procedure flown. This may or may not mean GPS, VOR, DME, LOC, and/or ADF may be required. It depends on the circumstances. Even the magnetic compass is not considered a navaid in an aircraft. It is technically a flight instrument.