You are talking about the Box Tops for Education Program. In the FAQ's page of their site http://www.BoxtopsforEducation.com/
it says the following:
"2. Is my school eligible for the Box Tops for Education program? The Box Tops for Education program is available to the following schools:
* Any accredited public, private or parochial school, for grades K-8, in the United States that is organized and primarily operated for educational purposes.
* United States military schools, for grades K-8, worldwide.
* Accredited home school associations, K-8, in the United Sates that are organized and operated primarily for educational purposes and have 15 or more students."
Accredited in this case might literally mean a homeschooling association or organization that is "registered" with the state of Indiana. But only individual parents can register as homeschooling (or not) so we can only assume that if your support group, association, or co-op can establish itself as an official entity, you can participate in this program.
Other subscribers to the IndianaHomeschoolers list said the following:
"Our homeschool group saves them as a group, and redeems them. I think they like you to redeem them in bulk, so maybe once a year?" ~Betty
"I'm not sure for how long, but if you need die-cuts or paper, there is a school in Wyoming who accepts Box Tops in payment for these. Go to http://www.dimeadicut.com
and check it out. It is a small private school and this is a fundraiser for them." ~Dwayla
"You can sell them on ebay, believe it or not!" ~Gale