Just a 'heads up':
I just tried to create a back up image with Shadow Protect but found that while a RAM disk was present, Shadow Protect would not 'connect', i.e. it wouldn't display the drives present on the system. As soon as I deleted the RAM disks, Shadow Protect would 'connect'.
It subsequently failed when backing up to a drive connected to a USB3 port, but it did work when the same drive was connected to a USB2 port.
It's a Shadow Protect problem, not RAM disk's.
J