For iSCSI there is project that that can make iscsi boot device from almost all network interfaces http://ipxe.org/
but this requires some skills and it can destroy the NIC if not done right. Some of the Intel NICs also offer this feature.
I would recommend a 10GbE for the Volume Replication to each DSS V6 and you can directly connect them also use MPIO w/ the ESX servers. See links below.

http://www.open-e.com/service-and-su...-to-resources/
Open-E iSCSI and NFS Failover
2011.11 Open-E DSS V6 Synchronous Volume Replication with Failover over a LAN (broadcast)

Others
2011.08 Open-E DSS V6 MPIO with ESXi 4.x