If you only want to copy the wallet file then everything should be ok, no matter what account you use.
If you need to run a program that's on the USB drive then a restricted account wouldn't help much.
Either you can't run any program there, not even malware.
Or you can run all programs on the USB drive, including malware.
Either way, you would be screwed.
With a restricted account the infection could only spread to files the account has write rights to.
Wow that's awesome.
So I can drag and drop wallet data files into and out of the USB drive and have no problems?
Also it's not possible for a virus to sneak in if I don't see the file in the USB?
Next !