MT7601U has been enabled in kernel config since pre-LE days (OE) and should just work as I remember adding it. Most Atheros/Railtek chips are upstream and also supported, but perhaps are missing firmware. Occasionally the USB device IDs aren't mapped in the driver (hence it doesn't load) but that's not common on older chipsets as the IDs have mostly been added upstream long ago.
Do the USB ports work if you connect a keyboard (checking for dead ports)?
If yes, run "dmesg | paste" after a clean boot and connecting devices to USB ports, so we can see what the kernel logs - if anything - and share the URL(s) generated.