We do have the same recommendation (of using two subnets with iSCSI) in XtremIO. It helps from a performance perspective (more concurrency) as well as another form of HA.
Client has VNX 5300 attached to multiple ESX hosts using EMC's best practices for VNX iSCSI configuration.  i.e. the iSCSI connections are established on two subnets.  Now, XtremIO is going to be introduced to the environment, and attached via iSCSI.  Can the storage controllers' iSCSI connections be implemented on these two different subnets, or, do all iSCSI connections need to be on the same subnet?  Have to believe that this is an increasingly common question in EMC shops.  Hopefully, the answer is documented somewhere.  Thanks, Eric
XtremIO and VNX in same iSCSI network