Yes, you can pull this off. To demonstrate a few of the ways, we'll return to Chapter 2.3's Cook who serves you after your return from battle in our hypothetical WWII game. He doesn't see his friend Tom in line for the grub.
Dialogue Deepening Techniques can add depth to the Cook, even though he speaks just one line of dialogue.
COOK (worried): You seen Tom? Just don't tell me he took a bullet too.
Remember that just because a character or even a line of dialogue conveys a sense of emotional depth, that doesn't make the character or the dialogue interesting. Techniques to make characters, dialogue, relationships, moments, or stories deep are completely separate from those that make these same components of Emotioneering interesting.
If you made the Cook's worried line "deep" but not interesting, it would be weak dialogue. For example:
COOK (worried): I don't see Tom. Was he hit?
The two lines are very similar. They both convey the Cook's worry, but the first one is more interesting.
Sure, it's more interesting in that it picks up more of the flavor of spoken speech, but, as explained in Chapter 2.3, what truly makes it more interesting is that we sense a personality in the first example. The second offers no such glimpse of a definable personality. In the first example, we can at least gather that the Cook feels close to Tom, that he hates hearing bad news, and that he hears a lot of it. All three of these qualities are missing in the second example.
Thus, when it comes to any kind of Deepening Technique, including Dialogue Deepening, it's not a matter of making an element deep or making it interesting. Rather, when you choose to make an element deep, you almost always need to also make it interesting. The side effect of trying to do these two things (make the dialogue both interesting and deep) is that keeping the lines short is harder.
Remember, although making NPC dialogue interesting is worth striving for in almost every case where it's possible, making NPC dialogue "deep" is optional a tool to be used when appropriate.
Let's try out a few other NPC Dialogue Deepening Techniques on our Cook.
COOK (looking over the battered and weary men; cynical): How's "the cause"?
COOK (regretful): Tom was still limping. I shoulda' stopped him from going.
COOK: Sorry about the slop. Up all night with the wounded.
Wisdom or Insight
COOK (downcast): You know, our kids won't even care about this war.
The Cook's wisdom is a Dialogue Deepening Technique. In the next example, I've given an NPC Wisdom, in addition to a second Trait, Bitterness, in order to make him more interesting.