If they can import foreigners, they can surely import students!!! Bet a lot of high school and college kids would love a summer on the cape.
Sure they could. But, that requires some sort of clearing house structure.
Under the current system, if a local supermarket needs some help, they likely go to some sort of clearing-house, and get connected to some overseas person who is connected to the H2B program through some sort of funnel in their home country.
If a traveling summer work corps clearing house could be set up, and American kids would do it, then there'd be no need for the existing system. But, without some sort of clearing house for the domestic program, I don't see how it could compete with the current system. Even, if its more desirable from our point of view.