As I understand it, a PC floppy drive will not work, unmodified in an Amiga, as there is some extra circuitry on an Amiga drive to allow it to do some clever things.
As for the icon appearing on workbench, that is interesting. I have never booted to WB without a floppy drive being physically attached, whether it has a disk in or not, so I don't know if the floppy icon is there whether a floppy drive is present or not.
