I suspect it depends if we're talking fault from an insurance or police point of view. The brake lights scenario I've had happen to me when driving slowly through down (missed the car, just), but even with perfectly legal spacing there is a marked difference in reaction times.
Technically probably it would be, although more likely a 50/50 on insurance and them doing that would (or should) be frowned upon by the police as they are driving without regard for other road users.
As for proving the lights scenario - the easy way is if the brake lights are smashed. When the glass shatters, if the lights were on then tiny fragments of the glass embed into the red hot light filament. Ideally this needs to be collected as evidence by the police however, but it has been used to convict in the past.
Now as for the reversing one - that's quite popular as an insurance scam for claiming wiplash, but the same trick can be used with the reversing light bulbs....if you can convince the police to turn out and take the evidence.
The sudden stopping thing is used a lot in insurance cons, even with whole minibus loads of people. Preston seems to be the place where it was invented (along with pretty much every other car insurance con in the UK), and it's still popular all around there, but I did hear of a case of this on Dartmoor of all places.