so your blkid output shows that blkid can detect it, and if you are able to mount it with devkit-disks --mount, then I guess gnome is just confused about the device not having any filesystem in udev (not knowing that it can call FilesystemMount() nevertheless).
Can you confirm this with
udevadm monitor --udev -e >/tmp/udev.log 2>&1 &
gvfs-mount -li >/tmp/gvfs.log 2>&1
then do the devkit-disks --mount /dev/fd0 in another terminal, then go back, press Control-C, do "fg", press Control-C atain, and attach /tmp/udev.log and /tmp/gvfs.log? I'm interested whether there is a file system in udev.log after that, and how gvfs responds to that.