What's great about this show is that for the first minute or so of Carmen's appearance, you can forget about the rest of the corps entirely and enjoy the presentation of the story. The guard's role playing here is top of the line, and the periodic use of spoken words is really smart. You have to really listen for them, and they tell you just enough about what is going on without ever approaching the cheesiness of full corps singing, narration, or even "drumspeak" (which, as much as I love the Bluecoats this year, is pretty annoying and sounds like it's trying really hard to be cool).
So Carmen is by no means a distraction. They integrate the guard as such so that it would turn your attention to what was happening in the guard at the time. And with the way I see it, any time a corps dosn't tell you where to look for important show events indicates a failure in the design of the show. (There are a few great examples of this being successful this year: Look at Bluecoats, like halfway through the show. The upper brass winds up into that little traingle on field-right, and the pauses while guesturing toward the guard on field-left while they do some cool flag work).