This is working as expected in LUN environments regardless of the Hypervisor. Because of the file system installed on the LUN (NTFS in this case) the space saving due to deduplication is not reported. You can however leverage this gained space by either;
1. Make the LUN larger without growing the Volume
2. Adding another LUN in the same Volume using the new space
3.Shrinking the Volume releasing the space back to the Aggr and then Creating an additional Volume and LUN.
I would recommend #3 for the Easiest and most flexible operation but all 3 are good options.