So as you can see, the FILE must be sent from the US, but the ARTIST must not. It's nonsense. And because the artist is unsigned, as HMX said, they'll have to do less work to be in the clear ;)
To be specific, to submit a song, you must be a resident of the U.S. Where the band is from has nothing to do with it.
Of course unsigned bands can submit songs! You have to own the rights to the material. Unsigned bands will probably have to do less work to make sure their material is in the clear.