The speaker in "Dulce et Decorum Est" is horrified by unforgettable images of death and of the dead. The same is true to some degree in Macbeth, particularly when Macbeth thinks about the dead king and, later, when he believes he sees the dead Banquo. Both Owen's speaker and Macbeth find themselves caught up in horrific situations. The key difference, of course, is that Macbeth is largely responsible for the horror he endures and for the horror he inflicts on others.
Both have man vs. man conflicts, where characters are fighting each other. There is also a man vs. society conflict in each, regarding the situations that cause them to fight and their lack of control over their fate. There is also man vs. technology/supernatural. In Macbeth we have man vs. supernatural, and in "Dulce et Decorum Est" we have man vs. technology.