If you're not in a wheelchair and want to take a helicopter ride; most companies will not decline you if you can sit upright and stay comfortable on a seat.
If you're wheelchair bound but still have mobility, then this will depend highly on the helicopter model in use for your flight.
If its a small, three seater-helicopter of limited space, this will make it difficult for you to access and exit the helicopter.
But if you're limited to a wheelchair only with no mobility; its highly likely the company won't be able to comply with your wish, as helicopters do not take on wheelchairs.