I don't think that's right- i heard that the exam papers get sorted by texts/questions into bundles of around 20 papers. At the marking centre, these smaller bundles are then distributed to teachers after ensuring that they don't have their own school etc.
So if you're in a cohort of around 150 like i am, then it's likely that not all your papers will be marked by the same people.
On the original topic, no the chances of getting caught are not that great, but this is an example of small possibility, large risk. If you get caught, i'm sure you'll get 0 for this paper, and probably won't obtain a UAI due to 'malpractice' of some sort.
A few similar phrases, especially in essays, won't matter- could just be a phrase the teacher likes to use.