Are helicopter pilots required to use GPS navigation?
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.