Here's a verbose rundown of the call that fails:

tristan@head:~$ sudo grub-probe -v --device /dev/md0 --target=fs_uuid
grub-probe: info: cannot open `/boot/grub/device.map'.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd2 is 586072368.
grub-probe: info: the size of hd2 is 586072368.
grub-probe: info: the size of hd2 is 586072368.
grub-probe: info: the size of hd3 is 586072368.
grub-probe: info: the size of hd3 is 586072368.
grub-probe: info: the size of hd3 is 586072368.
grub-probe: info: the size of hd4 is 586072368.
grub-probe: info: the size of hd4 is 586072368.
grub-probe: info: the size of hd4 is 586072368.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd6 is 586072368.
grub-probe: info: the size of hd6 is 586072368.
grub-probe: info: the size of hd6 is 586072368.
grub-probe: info: the size of hd7 is 586072368.
grub-probe: info: the size of hd7 is 586072368.
grub-probe: info: the size of hd7 is 586072368.
grub-probe: info: the size of hd8 is 586072368.
grub-probe: info: the size of hd8 is 586072368.
grub-probe: info: the size of hd8 is 586072368.
grub-probe: info: the size of hd9 is 586072368.
grub-probe: info: the size of hd9 is 586072368.
grub-probe: info: the size of hd9 is 586072368.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd0 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd1 is 156301488.
grub-probe: info: the size of hd2 is 586072368.
grub-probe: info: the size of hd2 is 586072368.
grub-probe: info: the size of hd2 is 586072368.
grub-probe: info: the size of hd3 is 586072368.
grub-probe: info: the size of hd3 is 586072368.
grub-probe: info: the size of hd3 is 586072368.
grub-probe: info: the size of hd4 is 586072368.
grub-probe: info: the size of hd4 is 586072368.
grub-probe: info: the size of hd4 is 586072368.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd5 is 625142448.
grub-probe: info: the size of hd6 is 586072368.
grub-probe: info: the size of hd6 is 586072368.
grub-probe: info: the size of hd6 is 586072368.
grub-probe: info: the size of hd7 is 586072368.
grub-probe: info: the size of hd7 is 586072368.
grub-probe: info: the size of hd7 is 586072368.
grub-probe: info: the size of hd8 is 586072368.
grub-probe: info: the size of hd8 is 586072368.
grub-probe: info: the size of hd8 is 586072368.
grub-probe: info: the size of hd9 is 586072368.
grub-probe: info: the size of hd9 is 586072368.
grub-probe: info: the size of hd9 is 586072368.
grub-probe: error: out of memory.