Per RADC-TR-80-299, the factors which had the most impact into the development of the ARW environmental factor are random vibration, sine wave vibration, and temperature shock. Random vibration and temperature shock were also important factors for the airborne fixed wing environments as well. The one major difference between the rotary wing and fixed wing environments is the impact of sine wave vibration. If your vibration dampening design minimizes the impact of both random and sine wave vibration, then you may be able to support modifying your environmental factor. Otherwise, the ARW environment would still remain appropriate.
If you have flexibility in your reliability prediction approach, you may want to consider the 217Plus methodology. This methodology uses the actual expected operating temperature, temperature cycling rate, and vibration levels as inputs to the failure rate models.