At the moment Hibernate has no support for LockMode.UPGRADE on databases that do not offer explicit support for it. It should be possible to support it on any db - at the expense of performance.
select ... from x where ... for update
one can use
update x set c = c where ...
select ... from x where ...
The Versant Open Access uses the same strategy: http://downloads.hemtech.co.za/jdo/manual/transactions.html
(10.2.1 Locking Mode)