Since it is freely available from rio's ftp site wouldn't it be safe to assume you can distribute it?

This ought to be true, but for some reason isn't. Besides, the Home PNA driver wasn't written by Sonic Blue, let alone by Empeg, and we don't get to vote on its licensing conditions. If the worst comes to the worst, you could always distribute a script that FTPs the whole shebang from Rio's servers, hoiks the driver binary out, and installs it wherever your software needs it.

Peter