I am not the network guy at my office, but if you look at his code it uses special DNS records (look-up Zeroconf, it is a discovery protocol for services on a network). Do you remember using Apple iTunes back when you could share music with people on the same network? Same difference, so to speak.

If your VPN provider, you or otherwise, does not block the mDNS/Zeroconf network traffic and had a permissible DNS configuration (almost all commodity routers have mDNS/Zeroconf config available if not on by default), I am sure you will have this work. The author can answer you more clearly.

It depends on how the VPN is setup... Multicast DNS will work if you are in the same L2 domain. Otherwise, a different solution is needed. For example, if you have a smartphone that you bring with you to the office, and that is connected to your office Wifi network and your home Wifi network, then synchronization would still work through your smartphone. Otherwise, a cloud-based "reflector" is needed. See the other comment about that.

And to apologize: re the reflector, I assumed you were doing this, like BitSync, and that is why I question ed you in my first comment. I am glad you do not over-promise with tyour project. Good work.