Every Node in a NiFi cluster run with their own repositories, flow.xml.gz, and work with their own set of data. Nodes in a cluster are unaware of what data other nodes in the cluster are working on. Once a cluster coordinator is elected all nodes send heartbeats to that node. Nodes cannot share repositories.
When you access the UI via any Node in the cluster, the UI will show the cumulative stats of the entire cluster to the user. The centralized management aspect comes in to play here. Any changes you make within NiFi (no matter which node UI you are logged into) will be replicated to all nodes in the cluster.