if you install WAD to the internal Wii/vWii memory, you can move them to the official "SD menu" allowing you to install more than 512MB of data to the Wii.
You can then launch them from the SD menu (no need of USBLoaders), but they are not really launched from SD menu, they are silently copied into internal memory and launched from there.
so you need at least 40MB free on internal to be able to launch game.
when you launch another game, it deletes the "invisible channel" on internal memory and replace it with the new game.
To be able to launch games from SD menu, you need a patched IOS 70 (Wii) or 80 (vWii)
I talked about EmuNAND because you mentioned USBLoaderGX !
and USB Loader GX can't launch games installed on SD menu ! remember, they are not "launched from SD menu", they are stored encrypted with your unique console key waiting for you to use the SD menu to "silently copy one at a time into the internal memory" before launching it.
using the official Menu or Sd menu has better game compatibility, BUT you risk bricking your vWii.
be sure to follow guides to make a vWii NAND backup so you can restore it if you ever brick it.
also, restoring vWii NAND will delete all your savegames so be sure to backup them regularly using the official "data management menu" to SD card.