I would kind of say that a Line Check Airman is a combination of a military IP and a military EP. A military instructor can only instruct and get non-current guys recurrent. A separate evaluator actually gives checkrides/evaluations. On the airline side, the LCA pretty much does both.

And of course, a military EP can also be an IP and be designated as either on any specific flight. In other words, the EP would probably be listed as an IP on a flight that he is not giving an evaluation on.