Hi Sylvain,
There should be no problem to have "fatload mmc 0 0x200000000 ${ramdisk_image}" command be included in this case. The boot process is supposed to be safe even if ramdisk_image doesn't exist on SD card at all (you will see a warning or an error complaining that ramdisk wasn't found but process won't crash).
Could you please provide more details on what are you trying to do ? Are you just following the instructions provided in the guide to test the flow or are you doing some customization ?
Thanks,
Roman.