We have a daily process that creates a CSV export file (from IC), and that file is manually uploaded into NK every morning. We know the upload could be automated, but our food service people like to be able to see what gets changed each day.
We use the FRAM module in IC for processing forms, so IC is the data "hub" for eligibility determinations.
Many years ago we processed forms in NK and sent the eligibility status back to IC and found that caused more trouble than it was worth when it was time for state reporting. But we've gotten better at automating exports now - plus we're not syncing directly with the State database anymore - so I guess using NK as the hub would be less of an issue, as long as the data flowed back to IC in an automated daily process (i.e. so that IC would be almost always accurate for the purpose of the Economic Disadvantage uploads to Synergy).
So the key here would be having a good process for achieving that sync. One issue to be wary of, is to avoid changing eligibility start dates, because that might get IC out of sync with Synergy... I think Synergy identifies unique records using a composite of student stateID and start date, so if the start date changes, Synergy see it as a new record with a date overlap as opposed to an updated start date... which would more than likely cause a range overlap error on the Synergy upload.