FAS2750 models have internal storage so in order for them to share disks this loop is necessary. They use storage cables which are slightly different from mini SAS.
Cluster Interconnect cables Part number X6566B-05-R6 (112-00297) or X6566B-2-R6 (112-00299). You can reference the install manual for this specs. The backplane connection is solely for HA connection, not a cluster connection.
It should not affect the failover of the nodes since there is an internal connection for both the nodes to the disks. That being said, it would be best if you cabled them together like the links below suggest since this will give you two paths to the disks (multipath HA).
Setup instructions (also lists the part numbers for the cables in stage 1)