It is possibly to set up trackers that work entirely inside Tor, using a piece of shim software that creates a virtual network interface with an IP mapped to your public/private Tor keypair called Onioncat https://www.onioncat.org/
I believe there are active trackers inside Tor that use it, but not sure
> OB is designed specifically to disallow onion routing.
That isn't the reason for UDP. NAT traversal is. If everyone was on ipv6 UDP wouldn't be used.
> Again TOR will not work with OB.
UDP can be tunneled through Tor hidden services
Yes, but not natively. As a SOCKS proxy applications need to use it specifically, but there are other projects which can give it a VPN-style network adapter like https://www.onioncat.org/