Not sure this is a widely known fact, but one of the changes we made in OWB 10.2 (and up of course) is the extensive support for complex Oracle data types. Areas such as spatial data will benefit from this of course, but now even simple complex (if that exists) data types are a piece of cake.
You can import or define user defined database objects in the data object editor. These user defined database objects now inlude things like Varrays, nested tables and object types. OWB also handles nesting types within other types.
If you are on newer database versions, you will also be able to use things like data and timestamp and other simple new data types. One of the things we have not yet completely done is to update the Long data type support. That is actually going to be on the list (no promise) for the next update of OWB.
Some of the above is covered in this whitepaper. It has much more interesting information around data modeling and support for modeling database features such as partitioning, materialized views etc. Again, many of these areas are going to be updated in upcoming releases of OWB.