If you are setting it up for "Maximum Capacity" you are basically setting it up as a software spanned raid, jbod, or windows dynamic disk, whatever WHS does under the curtains I am not sure.
In order to get any sort of "real" redundancy out of your disks, at least for backups, you would be getting at least one less disk worth of space out of it, for example, if you had 4x100gb disks, the most you would be able to USE, if there was any sort of actual redundancy involved would be 300gb. If you wanted to do this though, I highly recommend using hardware raid, most of todays motherboards have this built in.
Even if you were not using the maximum capacity layout in WHS itself, though, it would only duplicate share data, not backup data.
From a "home server" perspective though, you really shouldn't need redundancy in your backups. If you lose a backup, you take another one, if you lose the computer you backed up, you restore it. If you want more redundancy than that, you'll need to look beyond WHS.