Well, short answer is not really, but at the same time yes, if that makes any sense.
To be honest, lets assume the system is cracked, wide open. It still really is not practical to run backups off a disk , the price of BD-R media + burners, although has dropped, is still high. Since you can run a backup with relative ease from hdd/usb/network, it would be a moot point.
However, the issue then lies with how far is the system cracked - enough to run unsigned executables, or more along the lines of a drive mod. If it is unsigned executables, then the above is true.
If it is a drive mod however, then more work would be needed. We know the PS3 has a few special sectors (among others) that govern the disk layer crypt, but even after that is gone, the executables have a flag in them, basically a media check, that wont allow the decryption of the executable unless its being run from a legit, pressed disk.
Which in turn, goes back to #1 - opening the system.
So, its not really a clear answer, but hopefully that gave you some insight.