What are you talking about? You can't operate on disk images with diskutil outside of the few commands diskutil image gives you. For example, if you need to check whether or not a disk image is encrypted, you can use hdiutil info and hdiutil isencrypted. If you use diskutil image info, you may be prompted for a password, which doesn't make sense to handle in a program.

A disk image is not just a fancy disk. Disks and disk images operate on different planes, which is why the distinction between diskutil and hdiutil exists.