It's totally okay for people to work on similar nostr ideas and goals. They may approach it from a different angle, or use different technologies. 

As long as they know about each other, they will influence each other. If the code is available to look at, they can see how the other dev did something. 

It isn't necessary for them to be buddies or be in tight communication. 

Also, people like you (story teller of nostr) can help with that process of discovery by writing and talking about projects so that devs are aware of them.