If they can export it as OVF, you should can import it into workstation, and when done with it you can export it as OVF from workstation if you need to. Exporting it back to them probably isn't recommended, but the option is there, depending on what you plan to do.
You can also just take the VMDK if they want to go into the datastore and download it. You would have to create a new VM and mount the VMDK. This is probably more work than it's worth since the VMDKs are the bulk of the size of a VM.
It would be easier if they just export it as OVF.
From Workstation 14 you should be able to go back to VM hardware version 5. If the customer's VM was created in vSphere 5, it probably has hardware version 8, but it might be a good idea to double check what version it's running before they do the export.
