I don't know of the competition, so obviously I've got no way of knowing if this was the piece the pianist played, but the only non-basic transcription I've seen of the Hebrides Overture is by Heller, and is the first (Etude caprice) in the set 'Two Caprices on themes by Felix Mendelssohn, Op. 144'. I've never found time to try it out at the piano, but the score looks fairly heavy duty.