There are some DMC's who aren't defensively minded, or do well in defensive positions. These are usually more creative/technical players (Pirlo). You find these types of players in 4-2-3-1 as part of the 2 defensive midfielders. So even though you played DMC doesn't magically mean you can play as a DL/DR.
What I'm trying to say is if the player in DL/DR is trained as DMC (the defensive kind).