It is likely that some Wii related backup software can convert, or rather import .wia disk images to a WBFS format. The main advantage of this conversion is the reduction in file size that the WBFS format allows, as Wii discs are filled with padding data that must be present in the ISO but that the WBFS file system can strip away.
This can allow some smaller games to go from a 4.7 GB (4.37 GiB) ISO file to less than a hundred megabytes as any unused space on the disk will be filled by this padding data.