JPA scanning isn't very "thorough", so if the domain model entities are in a different location/component, JPA does not find them. An easy solution is to use Spring to scan for the @Entity annotation on the classpath and add any found to the persistence unit.
sidaof has a class to do so, EntityPersistenceUnitPostProcessor.
To use, configure it as a Spring bean, adding it as a persistenceUnitPostProcessors definition to the entityManagerFactory bean definition. For exampmle:
<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
...
<property name="persistenceUnitPostProcessors">
<bean class="net.sf.sidaof.spring.EntityPersistenceUnitPostProcessor">
<property name="packages" value="com.mypackage.domain" />
</bean>
</property>
...
</bean>