It would really depend on what the text is. The issue is often the stimulus texts are extracts not complete texts, so I guess there is not a lot that can be taken. The depth of study may indeed be lacking.Well, I guess it would probably depend on the marker, though I would definitely not recommend it unless you couldn't think of anything else.
One of my friends did take one of her related materials from either our Trial or Half-Yearly examination and has been using it since without the teacher minding, but that is a different situation.
I suppose that perhaps if the markers didn't recall or realise that it was the stimulus booklet text it would be fine? If they did they would probably mark more harshly.