1) In case you have an existing ORA_ROWSCN column in the database you should map this column to a field in your class and set the optimistic concurrency of the class to 'Backend'. The field should be set as the concurrency field for the class.
When you set the concurrency to 'Backend' OpenAccess will expect the ORA_ROWSCN column in the table. If not present, it will try to create it. To ensure that it is created the 'Update Schema' property for the class should be set to 'true' (in the Properties window in the designer)
Do get back in case you need further assistance.
the Telerik team