GeoServer does not come built-in with support for Oracle Georaster; it must be installed through an extension. Proceed to Image Mosaic JDBC for installation details. This extension includes the support for Oracle Georaster.
Adding an Oracle Georaster data store¶
Read the geotools documentation for Oracle Georaster Support: http://docs.geotools.org/latest/userguide/library/coverage/oracle.html. After creating the xml config file proceed to the section Configuring GeoServer in the Image Mosaic JDBC Tutorial