DNA cannot tell whether the sex was consensual or not. Unless the woman is pretty badly beaten, physical evidence that the sex was rape is often pretty thin.
Which, of course, puts it back into the "she said, they said" category, in this case. Although the driver might be a comparatively unbiased witness.
It is even harder to disprove rape than to prove it. Which is, IMHO, a dang good reason to keep your pants zipped.
One would think that a CO/Base Commander could and would make certain areas/establishments off limits in a situation like this.God knows that a drunken Soldier/Sailor/Airman or Marine can wreak all sorts of havoc during a sensitive deployment.
Rape in the PI can be charged when a customer doesn't pay, pays only a part of the agreed upon price or if the girl is jealous.