I found the answer to my question (below). The problem was an un-committed manual update to the db. Hibernate default isolation level means that such data can't be queried. A simple commit fixed the problem.

"I have Query object generated from hql. I set some parameters, call the list method, and get an empty list. If I execute the generated SQL in sql*plus, I get 3 records. Why would this happen? There are no filters or sql restrictions in my mapping files, and I have other hql queries on the same objects that do return results."