Answer is "it depends"
DAOS is server independant. Each server has its own data store for the .NLO files. So basically cluster replication happens "as normal". Message with attachment replicates, then DAOS kicks in and attachment is stripped. Not all servers need to run DAOS. A non-DAOS server can operate just dandy with a DAOS server.
Exception is in 851.
because the attachments are "read only" and filename is based on checksum value, they are going to be the same on DAOSified servers. In cluster servers on 851 (using DAOS) the servers check to see if the filename exists already on the cluster mate. If it is there, the attachment is not replicated.
Details here http://www.pmooney.net/pmooney/pmooneynet.nsf/d6plinks/PMOY-7XV2VF
Or if you click on http://www.pmooney.net/resources you will see a DAOS "step by step" guide that I wrote with Gab Davis (includes ID Vault too)