In the U.S. , ambulance specs/laws vary from state to state and city to city . 

I have never seen an ambulance flash its siren-flash with the headlights, it's always been a separate unit (beacon+siren combined unit or separate strobe units)

I can imagine driving with the headlights flickering all the time between high and low beam would be a major distraction to everyone, and blinding to other drivers on the road..

So i assumed it is some sort of manual "give way" signal (similar to the "quack" sound of the siren) that only sees short use

 Apparently . Depending on how the customer has us program their particular ambulance , I have seen some where the headlight flasher will function not only in "Primary" ( Vehicle in gear , engine running ) but also in "Secondary" (vehicle in park , engine running )  During a major incident , the truck may be sitting on scene for hours with the lights on .

Is the headlight flashing for long enough for this to be an issue ?

 There is/was a kit available for General Motors trucks which allowed for both low beams and high beams to be on at the same time . I've also seen that cars with Xenon headlights don't turn off the low beam when the highs are turned on  .

 Awhile ago , Ford sent us a mandate that we weren't allowed to operate the headlight flasher function on our ambulances when the headlights are on . We just programmed our system to cancel the headlight flasher when the headlights are on . Apparently , Ford was having issues with emergency vehicles melting both the wiring and the headlight housings because of this .

Aw thats unfortunate, I did find one!

LBD has some very very cool stuff. their shipping is definitely expensive though. im really hoping they don't modernize and/or trash their old stock

If it *must* be LED, I prefer warm white, 3500K and below.

I don't like the cold white or blue-ish LEDs some people like so much - it messes with my circadian cycle and keeps me highly alert.
When I had the early consumer grade LED lights in my workshop, it has happened a few times that I felt like it's 11 PM when in reality it was 3:30 AM already.

In my living room I have an 65W Osram Interna with a color temperature of 2650K and a CRI of 94 as a backlight.

In my sleeping room I have two dimmable 60W incandescent lamps

@Cole D. - The utilities around here will remove them when the lease is not renewed. The only indication left is a cut power drop, pole tag, or a thru-bolt that was left in the pole. Most lease lights are installed on existing poles...not often to see a dedicated pole just for a luminaire.