Thanks for the reply, but you are trying to solve a problem that doesn't exist.
If you run nntp.example.com and someone else runs nntp.example.org, and you both create the local group example.talk.general there will be no "collision", there will simply be same group on two different servers.
That is literally how Usenet functions; different servers carrying the same groups.
If the issue is you don't want posts from other servers on your server's local copy of example.talk.general, or vice versa, then you simply don't send or receive articles for example.talk.general to or from other servers.
Again, simply how Usenet/news servers work.
> You can have Usenet and Unusenet on the same server with no collision.
So what happens if someone creates the Usenet group un2.org.example.a.b.c which you already have as an "Unusenet" group?
Well nothing, because "Unusenet" is simply a word you've come up with to describe a standard, fundamental feature of Usenet: creating (local) newsgroups.