From the perspective of VCE:
- For the SACs - it could be very risky.
- For the exam: Given that you aren't allowed notes, and have no idea what the prompt is - I don't see how it can be too much of a problem (Other than it may not respond to the prompt).
So I think the chances of you actually writing the exact same essay as someone else is pretty minimal.
So in the words of Dr Karl: 'Plagiarise plagiarise plagiarise'!
Just do it discretely. And not in the SAC's.