The NAS code does not have to be the same. I would recommend you pause replication and resume it after the upgrade.
Hello, I have a Unified VNX5500 with file replication.    We are going to do an upgrade of the VNX5500 file code.   Does anything need to happen with the file replication side?   Do we have to pause syncronization or make sure that nas code versions are the same on each array?  The array that is being upgraded is the target side for replication.  Thanks,  Rip
NAS code file upgrade with file replication