The Ethernet Socket Interface is intended to be used when connecting Logix controllers to Ethernet devices which do not support the EtherNet/IP application protocol.
You definitely do not need Socket Interface to communicate between two Logix CPUs, either implicitly (Produce/Consume) or explicitly (Read/Write Messaging).
As to 'Raw socket' the two controllers to anything on the plant network, only the 1769-L30ER CPU has the capability to do so.
The older L43 CompactLogix will require a connected 1768-EWEB module carrying firmware 4.006 or later in order to acquire Socket Interface capability; the 1768-ENBT Ethernet bridge will not do.