I guess as long as the USB stack supports generic mass storage devices an USB floppy should work without problems.
However, as those drives have a built in disk controller, they're most probably dedicated to PC format - low level that is, so reading/writing Amiga HD format would be impossible.. I'm pretty sure they don't care about the high level format (=file system), so mounting it with FFS should be no trouble.
(Mac and PC share the same low level format on HD floppy, just the file system is different.)
