My configuration:

1) Ant target:

<taskdef name="hibernatetool"
classname="org.hibernate.tool.ant.HibernateToolTask"
classpathref="project.classpath">
</taskdef>

<target name="reverse" description="Produces XML mapping files from DB schema">
<hibernatetool destdir="${src.java.dir}">
<jdbcconfiguration
propertyfile="${basedir}/build/helloworld.db.properties"
revengfile="${basedir}/build/helloworld.reveng.xml"/>

<hbm2cfgxml/>
<hbm2hbmxml/>
</hibernatetool>
</target>


<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-reverse-engineering
SYSTEM "http://hibernate.sourceforge.net/hibernate-reverse-engineering-3.0.dtd" >

<hibernate-reverse-engineering>
<table-filter match-name="message" package="mapping_with_xml.from_DB_2_pojo.hello" exclude="false"/>

2) revengfile
<table name="MESSAGE" class="Message">
<primary-key>
<generator class="increment" />
<key-column name="MESSAGE_ID" property="id" type="Long" />
</primary-key>
<column name="MESSAGE_TEXT" property="text" />
<foreign-key constraint-name="FK_NEXT_MESSAGE">
<many-to-one property="nextMessage" />
<set exclude="true" />
</foreign-key>
</table>
</hibernate-reverse-engineering>

3) risultato di helloworld.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 15-gen-2010 11.19.22 by Hibernate Tools 3.2.4.GA -->
<hibernate-mapping>
<class name="mapping_with_xml.from_DB_2_pojo.hello.Message" table="MESSAGE" schema="HIBERNATE">
<id name="messageId" type="big_decimal">
<column name="MESSAGE_ID" scale="0" />
<generator class="assigned" />
</id>
<many-to-one name="nextMessage" class="mapping_with_xml.from_DB_2_pojo.hello.Message" fetch="select">
<column name="NEXT_MESSAGE_ID" scale="0" />
</many-to-one>
<property name="messageText" type="string">
<column name="MESSAGE_TEXT" />
</property>
</class>
</hibernate-mapping>

as you can see none of the settings put on revengfile has been taken into account.

I heard to put the default_schema on hibernate.cfg.xml but nothing changes.