I would not advise having the service wait for network.target rather thanpve-cluster.service. You need to wait for the cluster file system to start for the sync file to be present. Using network.target won't necessarily achieve this.
If you're...
I'd still personally go with Puppet-however...
Just make a systemd service one-shot that copies /etc/pve/priv/hosts after the cluster filesystem starts?
If you wanted you can then also set a systemd timer to call it every now and then. The...
I would typically approach this using Puppet to do the config management on the hosts. e.g. https://forge.puppet.com/modules/puppetlabs/host_core/readme
I appreciate most may not be running a Puppet / foreman solution though.