Phil,
Yes, you can migrate your data from a mounted disk image. I do have to join V.K in asking why, though. Unless there is some compelling reason to store that data in a disk image, it might be somewhat more secure to have that data stored "in the clear," as it were on a normal volume of a drive. Whether that storage be in the form of a "clone" or just a good copy doesn't really matter. What does is that you don't have the additional layer of complication represented by storage
within a disk image.
Again, there's no problem inherent in migrating from the disk image. It's a matter of keeping things as simple as possible, where the safeguarding of your data is concerned. If it is merely a matter of convenience, go ahead and use the disk image method,
but keep another copy "in the clear" normally, just in case. A disk image is a single file that, if corrupted, loses
all of the data that it contains.
Scott