Are you asking about WHS v1 or Vail? Your question seems to be about v1.
Backups range between full and incremental. In v1, see "Settings/backup" for how backups are created. If you delete old backups but keep at least one, it will be a full backup. The backups are stored in a folder separate from the pool,
though it occupies pool space. If you go to the WHS web site on microsoft.com, there are technical documents, including details on the backup folder, how to delete or copy it, etc.
In Vail, the backup folder is listed in the pooled folders, and duplication works on it the same as folder shares. How it will look in the next version of Vail without DE is unknown.