This post should help you understand how reliable VDP backup is, if protected virtual machines are migrated through various methods.
First point to note -'Migrate' option in web-client will be disabled while VDP backup is in progress on a vitual machine. The 'Migrate' option will be enabled once backup is completed. It means that you cannot manually migrate a virtual machine in web-client while VDP backup is in progress. However this does not effect the automated migrations in case of a DRS-enabled cluster. Virtual Machines with fully automated DRS can still migrate even if backup is in progress.
I have two different scenarios to mention.
1-VDP backup/restore after a protected virtual machine migrates to another host(vMotion)/datastore(Storage vMotion)/both host and datastore(Cross vMotion).
In the above case, VDP continues to backup/restore the virtual machines successfully without any problem.
2-VDP appliance itself migrates to another host(vMotion)/datastore(Storage vMotion)/both host and datastore(Cross vMotion)
Even in the above case after a successful migration, VDP continues to protect the virtual machines without any issues.