There is a replacement in Hibernate 4 and 5 but it seems like it is not really intended to be used outside of the Hibernate internals.

You need access to a SessionImplementor so you'll have to cast your Session to that. I can't find a way to get access that doesn't involve casting the result of getCurrentSession(). Then you can use the TransactionCoordinator to create an IsolationDelegate which works similarly to Isolater:

    SessionImplementor session = (SessionImplementor) sessionFactory.getCurrentSession();
    IsolationDelegate isolationDelegate = session.getTransactionCoordinator().createIsolationDelegate();
    isolationDelegate.delegateWork(new AbstractWork() {
        @Override
        public void execute(Connection connection) throws SQLException {
            // This will run on a separate connection with the current
            // transaction suspended (if necessary)
        }
    }, false);

One thing you can do is use the Hibernate action queue to register a specific callback that fires right before the commit or immediately after depending on your use case. Those classes are:

org.hibernate.action.spi.BeforeTransactionCompletionProcess org.hibernate.action.spi.AfterTransactionCompletionProcess

For your use case, it seems you would want to use an AfterTransactionCompletionProcess. In order to register the callback with a specific session you would:

session.getActionQueue().registerProcess( 
  new AfterTransactionCompletionProcess() {
    @Override
    void doAfterTransactionCompletion(
      boolean success, 
      SharedSessionContractImplementor session) {
      // do your logic here
    }
  } 
);