NANDroid backup/restore of CM11 encrypted device after wipe
Yes

As far as I know, a NANDroid backup makes an Image of the entire device.
So, this can work because the entire file system is copied along with the file system. The device will still be encrypted after restoring.

I might be wrong because I've never done this. But if you encrypt a flash drive with bitlocker, copy the contents of it including the encryption, format the drive and copy it back; It will still contain the data if you decrypt it.