It sounds to me like the powered pallet jacks might fall under the Powered Industrial Truck rules:
1910.178(a)(1): "This section contains safety requirements relating to fire protection, design, maintenance, and use of fork trucks, tractors, platform lift trucks, motorized hand trucks, and other specialized industrial trucks powered by electric motors or internal combustion engines. This section does not apply to compressed air or nonflammable compressed gas-operated industrial trucks, nor to farm vehicles, nor to vehicles intended primarily for earth moving or over-the-road hauling."
The ANSI code might be helpful as well: American National Standard for Powered Industrial Trucks, Part II, ANSI B56.1-1969