I feel like I should expand a little on what I said before regarding opting out of judging some styles. The exam, I think, is mainly to determine the judges level of ability to perceive and properly document those perceptions. Also to determine knowledge of brewing to some degree, and ability to articulate suggested tips on how to improve. Also to determine a judges ability to properly assign a score to a beer. The higher ranked a judge is, the more skill and knowledge they probably have. If a decent judge had the guidelines in hand, though he or she had never tasted a classic example, he or she will be able to do a fairly good job at filling out a score sheet. I'd rather get feedback from that guy than my BMC drinking, non brewing, buddy. But, if the judge's experience in that style is limited or nonexistent, I just don't see how they could decide who the winner is. They may be able to weed out faulty entries, maybe even forward the two or three most drinkable entries. But I for one would not feel comfortable at all if I had to assign gold silver bronze to a style I had never tasted before.
I've never tasted mead before. I think I could detect foul off flavors. I think I could tell you which one of a group tasted best to me. But there's no way I could give advice or win-place-show them. I am certain that no respectable mead maker would want my feedback or to find out that I would be deciding if his mead was a winner or a loser. If all judges would excuse themselves from styles they don't really know, there would be... world peace.