Hello franknstein, You can have both MD’s on the same network.  What you are going to have to do is to make sure that both units are not on the same subnet.  If both MD’s are on the same subnet then you will get corruption & can cause serious network issues.  Also you will need to get a couple of extra NIC’s so that you can configure the different subnets for each MD has a dedicated NIC’s.   Please let us know if you have any other questions.
I am interested in adding storage to a couple of existing file servers.  Currently these servers are using a dual-controller MD3000i [Powervault iSCSI SAN] connected via a couple of private network switches.  Everything is wired redundantly.  It works fine but we are running out of storage space and have maxed out the disk slots on the MD3000i.  I would like to know if it is reasonable to add a new dual-controller MD3220i by connecting it to the existing switches, configuring it on the same network but with unique port addresses, with the desired outcome being both MD devices are accessible to the file servers at the same time.  Is this a bad idea or a good one?  One worry is that the existing server NICs currently used to access the existing MD3000i maybe can't be used for accessing both iSCSI arrays at the same time?  In which case should we buy additional NICs so we have dedicated NICs for each iSCSI array on each server?    Are there any other potential issues you can see?  I'd appreciate any configuration advice.
multi MD3xx0i iSCSI units on one network