I guess I just don’t see the advantage of using a home-grown solution when there’s a lovely open-source library that will accomplish the same goals but is a more universal standard.
I’d rather have one “discovery server” to maintain then to try and maintain one for syncthing and one for zerotier, as an example.
I’d ask you to take a look at the documentation: https://www.zerotier.com/manual.shtml#5
Take a look at the NAT traversal options it has, and seriously consider if it’s doing a better job then you can do, especially with regards to NAT traversal and UPNP.