Either by way of direct mounting, or coupled external flash (cable, wireless), there needs to be an TTL flash "known" by the camera.
No, there doesn't. Second-curtain sync is much, much older than any form of TTL; it's as old as electronic flashes, period.
The problem with high-speed sync is due to the speed the shutter curtains travel, not due to the flash duration. All flash durations are much shorter than the fastest of shutter curtains. When you shoot at a speed faster than your flash sync, what happens is that the flash pulse has shot its wad while one of the pokey shutter curtains still hasn't cleared the sensor.
With a slow shutter speed, the one curtain completely moves out of the way of the sensor, the flash signal is sent, the curtains remain stationary for the duration of the exposure, and then the second curtain covers the sensor. With second-curtain sync, all that happens is that the flash signal is sent just before the second curtain starts to close rather than jut after the first curtain has finished opening.
With a fast shutter speed, faster than the rated sync speed, the shutter speed is shorter than the time it takes the curtain to get out of the way. So, even before the first curtain has fully cleared the sensor, while only a partial slit of the sensor is exposed, the second curtain already starts to close and chase the first sensor. Again, the flash is fired as soon as the first curtain has fully cleared the sensor...but much of the rest of the sensor is already obscured by the second curtain that's hot on the heels of the first.
High-speed sync gets around that problem with some sort of precision-timed jiujitsu that fires the flash multiple times while the curtains are only exposing part of the scene. How, exactly, the engineers figured out how to do that in a way that doesn't look weird is beyond me...but they did manage to pull it off.
And TTL metering is completely unrelated to curtain travel. These days, I think it's mostly accomplished by some sort of high-speed preflash, but there've been so many other sorts of methods used that I wouldn't quote me on that.