How can I map a table (or view) with no primary key?
Every table (or even view) should have some unique key. The mathematical definition of a relation is a set of tuples. (Sets do not permit duplicate elements.) Furthermore, truly identical rows can not possibly have any meaningful semantics from the user's perspective.

In some cases it may be sensible to go as far as mapping all columns of a view as a <composite-id/>, but there is almost always some smaller business key. (Note that Hibernate does not require that this unique key be enforced by the database schema, of course.)