The only with MTU is when you are using bigger packages than you have set in your network.
Example: All your network is set to 9000 MTU, but vSAN and NFS are still set to 1500.
This works without any issue, if you need to change vSAN to 9000 is ok. You just need to change the vmkernel to work with 9000. NFS vmkernel will still be working with 1500.
Now if you have a network set to 1500 MTU and you are changing any part to work with 9000 then you have a problem since the network cannot handle that packet size and will full queues will cause packet losses when transporting udp packets.