Why would an experienced T7 pilot need to practice approaches to DG. Even allowing for the fact that FS X is very unlikely to have an accurate rendering of the place it is dead flat, no obstructions, no complex approach no nothing . If he could land a T7 as his day job then he could land at DG without ever having to practice.
I think the only significance DG could have for this sad story is that it is one place where there will be an alert and active air defence radar coverage however it is actually provided and we would know if MH370 went anywhere within 500 miles of the place.