> I don't see how anyone can expect to operate a Tent server without such cooperation
You have to have a connection brokering service for locating servers and setting up connections.
The idea is that your content server goes out and connects to a broker server. The user's clients do this also. So if their client wants to set up a connection with your server then it sends a message to the broker. The broker then communicates back to your server, which then pushes a hole through your firewall using a mechanism like uPNP or starting a fake connection to the client to open up a hole in the NAT connection tables for the client to connect through.
All in all this is a relatively routine thing used by a huge number of popular 'p2p' protocols.
I am sure that the 'Tent' people took this into account. Personally I think that a modified Jabber server would be good for this sort of thing.