They plan to use their own disk subsystem with the filers instead of NetApp's, but this doesn't change the function of the product at all. It's still "Network Attached." Dell will continue to offer their own server attached products as well.
I.e., if the question in
(b) Is this going to replace Dell's disk subsystem? In which case the NetApp/disks are no longer a "network attached" system.
is interpreted as "will a NetApp filer be plugged in where a Dell storage system used to be plugged?", the answer is "no" - Dell's current PowerVault systems appear to be *disk* subsystems, with a RAID controller but with no file system or file access protocol, while NetApp filerss are *file system* boxes, accessed via NFS or CIFS rather than via SCSI or Fibre Channel.
Thus, Dell will presumably continue to sell PowerVault boxes as *disk* subsystems, but will also sell NetApp boxes as *file servers*.