Using a Spatial ColumnTo use a spatial column in a table you need to create spatial metadata and a spatial index. In SQL Developer you can do this by right clicking on the table and choosing Spatial - Update Spatial Metadata and Spatial - Create Spatial Index. At this point many standard tools will be able to query and display the geometry out of the box.
Displays a Oracle Spatial Geometry by just choosing the column. It is based on the Eclipse RCP (Rich Client Platform)
A useful plugin for SQL Developer which makes the creation of the index and metadata more simple. It has a viewer which is available within SQL Developer.
Validating GeometryTo validate a geometry column in a table you can use
select sdo_geom.validate_geometry(<column_name>, 0.05) from <table_name>
where 0.05 is a tolerance value.