I've done many photo flights in helicopters and I am unaware of any regulation that they must be above 500 feet. Most of the time I requested 400 feet to do my photography, but sometimes lower, and that was granted, though most pilots for the sake of safety and not because of any regulations wanted to keep moving and at 400 feet minimum. (I rarely needed them to hover).
(I think that the regulations currently leave a lot to interpretation. and operating in an area designated for UAS such as 400ft and below in my opinion is a "undo risk" and also from being a pilot dealing with a "partial" engine failure at 3,500 ft. in a fixed-wing aircraft. I personally would never want to have any catastrophic failures at 500 or less. That idea just scares me and is well below my personal minimums as a pilot with over 2500 hours. Unfortunately, some helicopters get confident and read only the first line of part 91.119(d). I would like to see the FAA put something in this part that gives them the responsibility to see and avoid or even minimize interactions with Drones. The US Forestry Fire department flew at treetop height over our building just the other day, and Law enforcement does it often with ADS-B turned off. At least the Forestry helicopter came upon our DJI Air Sense ADS-B display. Once Remote Id is an everyday thing I think in my personal opinion helicopters should have to have a UAS Remote ID system to prevent collisions below 500ft.
Again all of the above is not the companies but my personal opinion. I underlined the interesting parts.
Mike D.
-------------- Here are the regulations referenced below. --------------
§ 91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
(a) Anywhere. An altitude allowing, if a power unit fails,
an emergency landing without undue hazard to persons or property on the surface.
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open-air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
(d) Helicopters.
Helicopters may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section if the operation is conducted
without hazard to persons or property on the surface. In addition, each person operating a helicopter shall comply with any routes or altitudes specifically prescribed for helicopters by the Administrator.
Here is the "gotcha"
§ 91.13 Careless or reckless operation.
(a) Aircraft operations for the purpose of air navigation.
No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.
(b) Aircraft operations other than for the purpose of air navigation. No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.
ANOTHER INTERESTING TIDBIT.. perhaps they are flying under the other traffic (if you are close to an airport.)
§ 91.126 Operating on or in the vicinity of an airport in Class G airspace.
<snip>
(2) Each pilot of a helicopter or a powered parachute must avoid the flow of fixed-wing aircraft.