I've no idea whether that firmware would still be compatible with the control interface used by the Alpine, and the Rockbox FAQ doesn't tell me whether I could restore the iPod to its original firmware if it turned out not to be. (It mentions dual-booting, but I don't know if that would be good enough.)

The risk-free approach, I suppose, would be to borrow an iPod that already runs Rockbox, and test that against the Alpine. So. Are you mentioning it because you use it, or alternatively do you know somebody who does?