This documents covers the possibility of multiple connections to an X-gateway Ethernet/IP adapter
Can multiple PLC connect to the Ethernet/IP adapter side of an X-gateway?
Yes multiple connections can be made to the Ethernet/IP adapter but there are some limitations to the connections. Only one Class 1 Exclusive owner connection is supported. However additional connections can be made with Class 3 GET and SET connections. It should be noted that the PLC's are not aware of the others connection and there for can over write each other. Due to this limitation it is recommended to only read data for the second connection.
On the primary plc you will setup a exclusive owner connection, either with the EDS file or as a generic EIP device. See the following App notes for details.
For the second PLC get/set messages one option is to set up a read data explicit message. See the message instructions app note for details.