To answer a question with a question,  Why would you want to?  The primary driver on Celerra/VNX was to get access to bigger filesystems, right?  But with UFS64 the 16TB filesystem size limit is gone, and now you can do at least 64TB without a problem, potentially much more.  I would think that you're better off to consolidate those NMFS down wherever possible to simplify administration.  You could of course do the same thing on Isilon with a whole different level of scale.  10s of PB without a problem.  ~Chris
We used to be able to do this in Celerra and VNX.  Does Unity support nested mounted file system?
Can Unity Nest Mounted File Systems?