Hmm, well normally I just start with a "hello" or "howdy" and if the group is good, then there is likely not going to be much else said the whole dungeon until the final boss is dead.

Most of the time if you are DF'ing solo there's actually very little reason to talk, outside of making conversation or telling someone they are doin' it wrong, because generally speaking these other players are likely not even on your same server so you are not likely to ever run into them again and remember that you ran a dungeon with them before one time.

I do make conversation though, when I DF and actually get into a random DF party with people from my own server that I actually do know. It's a fun coincidence, and has actually happened to me a few times and is usually always fun/funny.