Julie is right -- the contest guidelines also makes it clear that all styles are welcome, both metrical and free verse, and the judges are also reminded of this, and it shows in the wide range of styles of the winning books. The last predominantly rhymed and metered book to win was in the 2013--Melissa Balmain's
Walking in on People. The 2014 winner, Carrie Shiper's
Cause for Concern is essentially free verse, with occasional use of very loose meter. And last year's winner, Emily Leithauser's
The Borrowed World, is as Julie described it--very few rhyming poems.
Cheers,
...Alex