You could try this, there is a good chance it will work and if it doesn't no harm will be done.
Create a new disk of exactly the same size.
Move the descriptior vmdk file into the same dir as the existing vmdk
Rename the vmdk file to match the flat file and edit to make sure it is pointing correctly
Then try adding the disk to an existing VM to see if it works.
If so create a new VM with existing disk.