@unknown56 The answer is its complicated but not impossible.
Lets take this one step at a time.
Is is possible to use a synology NAS or most other NAS’ that have nfs, and ftp support. I have a older tutorial on how to configure a synology nas for a storage node. https://forums.fogproject.org/topic/9430/synology-nas-as-fog-storage-node
Within FOG ecosystem, only master nodes (typically fog servers) can capture images from target computers. You can not capture images to Storage nodes. There is one way replication from a master node (fog server) to a storage node. This replication only runs on the master node or fog server. So you would normally have a storage group with the FOG server as the master node, and then add additional storage nodes to this storage group, as storage nodes. One way replication happens as expected master node to all storage nodes. (stick with me, I’m almost at the point). If you were to change this storage group to an unsupported configuration, where the synology nas was listed as a master node and the fog server was listed as a storage node, then the roles would be reversed. You could then capture and restore the files from the synology nas only. There would be no replication between the reversed roles of synology nas and FOG server since the replication service only runs on a real fog server. The only gotcha here is that the FOS Engine (software that runs on the target computer) connects back to the nfs share (on the fog server or synology nas) as user root. So when the nfs share is setup you will need to ensure that a user by the name of root can mount the share, this is typically done with a share level parameter of no-squash-root