Hi Pete,
Replication: Yes I have set both SEPM to replicate each other between Internal and DMZ
SNAC: not yet implemented, but soon to be for the Internal only, not DMZ
I've seen that the SYLINK.XML in my DMZ servers got
Priority 1: connect to SEPM Internal FQDN
Priority 2: connect to SEPM DMZ IP address
Priority 3: connect to SEPM Internal IP address