Can Tesla just unlock any of their vehicles thirdly and access the video

Almost always yes, but it’s the same for any modern car

Tesla allows owners to opt out of online services, in which case the video is stored locally briefly and Tesla cannot see anything from the car or do anything to it

Tesla employees got in trouble years ago for sharing sexy videos from random Tesla car drivers and passengers

So don’t do anything in or near a Tesla you wouldn’t want seen by randoms