It just works.
DaisyDisk automatically detects disks protected with FileVault 2 and adds
encrypted to their description. All further actions are completely transparent to users.
Technically, FileVault is an encrypted sparse disk image (which means that the image size is not fixed, unlike the
normal DMG file size) that contains your home folder. Consequently, most disk visualizers display the FileVault as a single opaque file or folder. While this is correct from the file system level, the users on contrary expect to see their home folders there.
DaisyDisk displays FileVault-enabled home folders exactly as normal home folders, like the Finder does. You don’t even need to know about FileVault.
FileVault-enabled home folders of other users can not be decrypted (even if you scan as administrator), and are always displayed as opaque files. You need to log in as the corresponding user in order to see content of his FileVault-enabled home folder.
Remember, that the size of the FileVault sparse bundle is always larger than the sum of files and folders it contains. This is not a bug of DaisyDisk, this is how things work :)