The part that matters for supportability is the system making the iSCSI connections, so the OS on any virtual machines doesn't play a role unless the virtual machines run (boot) off of a local drive (vhd/vhdx file) on the physical machine and they make their own iSCSI connections for any data drives, which is unlikely (no failover between servers).
If your company is going to rely on a 5-node Hyper-V cluster, I would suggest to also get a storage solution that is supported with the OS you're using for the hypervisor.
Staying with the Dell options (as this is a Dell board), for running Windows 2012, you'd want to look at an MD3200, MD3600, Equallogic or Compellent solution. If the budget doesn't stretch that far, I'd suggest to stick with Windows 2008 R2 for the hypervisor.
Note that Microsoft's free Hyper-V server 2008 R2 is also not supported per the support matrix.
You can find the support matrix and other MD3000i documentation here: www.dell.com/.../powervault-md3000i.