No, pre-paying gratuities is not required.
If you have been pleased with the services of your Journey Director and Driver, you may wish to express your satisfaction with a gratuity. As this is a matter of a private and individual nature your gratuity should be sealed in an envelope and given to your Journey Director and Driver at the end of your trip. A guideline of $6-$8 per person per day to your Journey Director and your Driver.