Currently, when Oracle12cDialect is used, an IDENTITY column is used for an entity ID when mapped with:
1) <generator class="native"/> using hbm.xml;
2) @GeneratedValue(GenerationType.AUTO) with hibernate.id.new_generator_mappings=false; (note that hibernate.id.new_generator_mappings=true is the default).

After this is fixed, Oracle12cDialect will use a SequenceStyleGenerator in these cases, consistent with earlier versions of Oracle dialect versions.