I'm just in the process of attempting to migrate to an Oracle schema, but am hitting this AmbiguousTableNameException problem too.
Working with one of our DBAs we've cut down the privilages of the user to a minimum but I'm still getting this exception.
I've noticed some posts on DBUnit boards discussing this exception and one possible solution seems to be to explicitly set the schema when connecting to the database. Apparently DBUnit has a habit of picking up table names from other schemas. I've tried doing this in the jdbc:oracle:thin connection string but without any luck. Does the schema get set explicitly in the TeamCity migration code?