Spring + Hibernate Transaction -- Native SQL rollback failure - sql

Question

I recently came across this problem -- my transactional method (marked as #Transactional) failed to do the rollback when I use native SQL. If I instead use Hibernate API to save an entity, it did roll back!
Background
I have a class Employee() and I have a table tbl_employee. I want to use native SQL to insert rows to tbl_employee, and each insertion will insert 500 rows at maximum. For example, if I have 600 employees to insert, I will create two SQL insert queries (one for the first 500 and the other for the next 100). My insert method looks like this (to make it simple, I only consider insertion of (500,1000) rows):
#Transactional
public void insert(List<Employee> list) throws RuntimeException{
Dao dao = new Dao();
String sql1 = buildSQL (list.subList(0,500));//the first 500. buildSQL is a simple method which build an insert query for the list
String sql2 = buiildSQL (list.subList(500,list.size()));//the remaining
dao.executeSQL(sql1);//dao performs the sql query to the database
dao.executeSQL(sql2);
}
And here is the spring configuration. I use HibernateTransactionManager.
<bean id="txManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory">
<ref local="mySessionFactory"/>
</property>
</bean>
My Dao() class performs my sql to the database and if there is an exception during insertion, I will throw a RuntimeException.
The problem
I tried to insert 501 employees to an empty table. The first 500 have unique ids and the last one has the same id as the first one. Therefore when I insert the last one, there will be a "DUPLICATE　PRIMARY KEY" error. I expect that the previous insert() method will rollback -- No rows should be inserted to the table. However, I noticed that the first 500 got inserted to the database!
I then tried to use Hibernate API. My insert method becomes:
#Transactional
public void insert(List<Employee> list) throws RuntimeException{
Dao dao = new Dao();
for (Employee employee: list)
dao.save(employee);
}
And it actually did what I expect! No rows are inserted to the database once there is an exception.
My questions
I wonder if spring/hibernate support transaction management for native SQL.
The rollback works if I directly "save" an entity using Hibernate.The reason why I want to use native sql is that I actually need to insert employees to different tables based on, say, the insertion datetime. (e.g the new emloyees this year will be inserted to tbl_employee_2015).Therefore it's easier to map to different tables using native SQL. Is there any other elegant way to handle mapping to different tables?
I am assuming that one sql for multiple row insertion is very efficient. Therefore I want to insert 500 rows by one sql. I don't want to do Hibernate save one by one in a loop. Is this assumption correct?
Thank you so much for your attention！