Not true. Ive told my insurers Adrian flux about both my in car tracker and camera set-up and they note I have it, but that it makes no change at all to my policy.
If some tool causes an accident and I have the video proof then I will present it, but if i'm at fault then its my choice, however genuinely if im at fault I would admit it, there's no point lying. Sometimes my camera genuinely doesn't power up (goes through the initial boot cycle but never stars recording, think its due to exactly when you start the car in the process), what if the day I have the crash that's my fault is one of those days?
The highway code is clear on this however. You are not supposed to take flashing the lights as a prompt to pull out, its to alert another driver you are there. If that's your only argument in court, the guy flashing his lights will win 100% of the time as its in black and white. I guess this is why they're doing it as technically its not really illegal, they could just be alerting you that they're coming and to not pull out.
Of course, in the real world (at least I) you wait for the flash and normally evidence of the car breaking and possibly even a hand wave, this would be caught on camera and could be used as evidence.