-The goal of uvnc2me was to create a free LogMeIn alternative.  A single exe that can serve as viewer or server. Something simple without the need to configure anything... 

Is the authentication done by the access servers ?
NO, the encryption is between the endpoints, authentication is part of the encryption.  
What does the access server(s) do ?
The access servers act like a dyn-dns server.
The access server tell the ip and port of the counter part with the same id.  
Do you need 2 access servers ?
We use 2 servers for loadbalancing and redundancy.
Do I need to known the ip adresses ?
No, uvnc2me use an identifier to auto detect the ip adresses.