The Secretary of the Interior (hereinafter referred to as the Secretary) is authorized to recruit, train, and accept without regard to the civil service classification laws, rules, or regulations the services of individuals without compensation as volunteers for or in aid of interpretive functions, or other visitor services or activities in and related to areas administered by the Secretary through the National Park Service. In accepting such services of individuals or volunteers, the Secretary shall not permit the use of volunteers in hazardous duty or law enforcement work or in policymaking processes, or to displace any employee: Provided, That the services of individuals whom the Secretary determines are skilled in performing hazardous activities may be accepted