Can you show the reference to the documentation?
My understanding is that the DHT is used to find what is the IP of the correspondant, as this IP can change when your correspondant goes offline. So your contact list has the hash identifying your contact. When you want to establish a communication, Jami asks the DHT with the contact’s hash to get the IP, and then it creates a session between your IP and your correspondant’s IP.
May be I’m wrong but that’s the way I imagine it works.