"Dead men" as a term refers to men who were condemned by The7. The title refers to how Kane and Lynch are "dead men" (Kane becomes one before the beginning, Lynch becomes one after Chapter 7, or at least says that he should be) as well as the dead men who Kane recruits in Chapter 8 (Thapa, Rific, and Shelley).
Many "dead men" were killed by The7 before the beginning of the game, and others went into hiding and could not be found.
The term "dead men" was spoken only once in the entire game, when Lynch asks about Kane's notebook:
Lynch: What's that?
Kane: A list, of dead men like me, disowned and ruined by The7.
Lynch: I should be on that list too...
Kane: The fuck you should! You don't want revenge, you just want to stay alive.
List of known "Dead Men "
- Rific (deceased)
- Grimley (deceased)
- Maddsen (deceased)