You can do a quick check in Neo Gamma to see if your USB HDD is being recognised, you can also boot games off the USB HDD from within Neo Gamma too.
You can use other loaders, USB Loader is not even the best loader, so try other options before being tied into one loader:
USB Loader Releases - WikiTemp
Read this thread to get yourself going, then look into other options that suit you:
Other game managers:
WBFS Managers - WikiTemp
And look into the choices of whether WBFS or FAT32 would suit you better.