Yes, there seem to be a lot of complete misunderstandings.
I know a lot of people are on the DF server and not HyperLobby
Most of the Servers in HL are actually Dogfight and
Only Coops are non-dedicated.
I want to what the DF client is
It is the UP3 Version of a dedicated dogfight server. It is not a game version you can actually use to play the game yourself, because it lacks all the graphical output. It's just a DOS-Box of the game. You and others can than connect to this dedicated server.
Just wanted to know if I would have to open up my network on the DF like HL
I am not sure about 'opening the network' for HL, but if you want to set up a dedicated dogfight server you have to open the corresponding ports in your router. Otherwise nobody will be able to connect to your server.
I don't think this is a big threat to your security.
I hope this helps a bit. If not, do as Emil said:
Maybe you make your questions clearer.