If one's battery is dead, will an EFI bike (such as a 07 Nightster) be able to be started with (clutch in, third gear engaged, coasting down hill) a bump start?
Depends on how dead the battery is. I've bump-started EFI cars on several occasions, but not when the battery was at 0. Remember that the starter is going to draw far more amperage than anything else on the bike, so even when there's not enough juice to spin the starter, there is often enough juice left to build some fuel pressure and allow you to push-start the bike.
It's going to have to be one hell of a hill. The gearing on the 04+ bikes doesn't much care of roll starts. It took three of us two tries to get mine going on a decent slope.