Crab,
The simple answer (without providing all of the justification and rules) is yes - if it is a private flight.
Helicopters are certificated for flight in IMC not IFR - some helicopter Flight Manuals do have a night endorsement but not all (which does not mean that it is prohibited); it is the operational rules that drive the requirements for crewing and equipment.
For commercial air transport (and with respect to JARs) it is the performance rule in Subpart I - Performance Class 3, which provides the proscription.
Jim