I don’t see why not. All you would need to do is write from the DCS to the appropriate data files in the SLC. Having said that, I don’t know anything about messaging to and from a DCS but if it supports PCCC messaging then it should be able to send data to and from the SLC via Ethernet/IP TCP. You might need to move the I/O data in/out of data files in the SLC but creating some “MOV” ladder logic sounds a lot easier then trying to reverse engineer a generic CIP connection (at least for me). It would also give you the ability to create some level of “intelligence” at the I/O level if needed. For example, if there is an alarm condition that occurs, you could program the PLC to deal with it (I.E. shut a process down?) rather than waiting for the DSC to do so. The advantage in that scenario would be that even if communications between the DCS and the SLC fails, the SLC could maintain a certain level of control and safety.
On a related note, it is worth mentioning that AB has put the 1747-AENTR and 1747-L55 (SLC5/05) on Active Mature status. There is no date set yet and it could be years but it’s worth keeping in mind.