i am gonna give a short answer, in trying to being direct and straight...
use
http://wiibackupmanager.co.uk/ to copy the games into the usb drive
it should be formatted as fat32, you can have it on ntfs but fat32 is better...
also, make sure to refresh the game list, some loaders (if not all) like wiiflow require you to manually reload the games list.. or they will show you the old list... (on wiiflow, you press home button and choose reload cache)
you can also try cfg usb loader.. it's my favorite..