Just a Heads up, Dolphin v 5.0-12188 ( almost a year and a half ago ) added support for WIA(Lossy) and RVZ(Lossless) formats for GameCube and Wii games.
Updating the systems section in emulators.xml as follows should add support.
<Emulator name="Dolphin" hidden="false">
<Systems>
<System name="Nintendo Gamecube" option="" script="false" cmd="-e "%path\%file%ext" -b" extensions=".rvz,.wia,.ciso,.dol,.elf,.gcm,.gcz,.iso,.wad,.wbfs"/>
<System name="Nintendo Wii" option="" script="false" cmd="-e "%path\%file%ext" -b" extensions=".rvz,.wia,.ciso,.dol,.elf,.gcm,.gcz,.iso,.wad,.wbfs"/>
</Systems>