it seems to me a bad idea to have two ip addresses on one device in one L2 domain

I agree, but it is a temporary limitation I`m trying to work with the get replication working while waiting on a dedicated replication network. 

Hello
this is the link to replicate between data domain through an interface
dedicated.

Article Number: 000077882
https://www.dell.com/support/kbdoc/en-mx/000077882/managed-file-replication-over-a-specific-interface

you need to create routes to manage, backup and recover data, and a route to only replicate data.