I've just been reading section 8 of the Hibernate reference (2.1.7)

It mentions three ways of mapping objects to a relational database, but doesn't say anything about databases (such as Oracle and PostgresQL) that can support object storage and polymorphism natively.

Can someone please add something to the manual and/or FAQ to state Hibernate's attitude to this type of database? Does Hibernate not make use of these features at all?

Is there any reference or pattern for developing an EJB application around an OO database?

Hibernate does not support proprietary "object-relational" (a very misleading marketing term, btw) extensions. If you know how to use it in JDBC, you can write Hibernate extensions to use a particular feature.

Read "Introduction to Database Systems" by Chris Date. There are no "OO" databases, this is again marketing talk for outdated network and hierarchical databases from the '60s.