While it is currently not possible to upload Groups into the Participant Address Book, it is possible to organize the contacts into groups after the contacts are added to the Address Book.
  1. Add all of your contacts into the Participant Center via upload.
  2. Once the contacts are under the Individual tab, mark the boxes next to the contacts you want to organize into a group.
  3. Select "Add to Group".
  4. Select the "Create a New Group". Enter a group name and select submit.
  5. Toggle to the Group Tab and select the group name to see the members in your group.