I've been to Onikoube fours times so far in the 2010 season and the conditions varied each time. The first time was decent with a nice amount of snow and only intermittent ice patches. The second time was extremely snowy and had frequent whiteouts. The third and fourth time was very icy, which meant pain during every fall.
The resort itself is on the small side, but it's cheap and a one day pass comes with a 1,000 yen food voucher