This is a tricky one to answer conclusively.
Most insurers will consider this to be an ambulance charges. If a helicopter is used as an ambulance because it is the only way to get medical attention to someone on the side of a mountain then this should be included within the medical expenses cover.
This should not be confused with Search and Rescue cover. If a person is lost and helicopters are sent to find the person (injured or not) then these costs would not be covered.
Hope this helps.