For Wii, this works for me:
exe=org.dolphinemu.dolphinemu/.ui.main.TvMainActivity
romextension=wad,iso,rvz,wbfs,gcz,ciso
parameters=
Your exe line is a bit different from mine. I also keep the parameters field empty. If you open the Hyperspin menu (R+L+R3+L3) and select the emulator there, it will generate the correct launch parameters for you.