I'm not convinced a couple of random miners, engineer or not, would have been a cornucopia of technological data. But it's also doubtful there ever were any people staying aboard the drill - it's way too small to actually hold any!
A perhaps more likely scenario would involve Nero noticing the saboteurs and beaming down a couple of expendable musclemen who'd then immediately emerge from that hatch. The drilling prevents "broadcast" beaming, but Nero would have been using "cable"...
As regards Khan's role, let's remember that it is Khan himself revealing that role. The egomaniac might have seriously believed he was the only arrow in Admiral Marcus' quiver, or at least would have tried to pass that impression to Kirk, but in reality Marcus probably was working on a much broader front (and barely remembered Khan until the London attack). Khan may have offered input on how to build the dreadnought-class vessels, but a dozen other evil supergeniuses may have been employed as well, not to mention other shady assets.