Bad glow plugs may show 0 ohms, or, more likely, they may show infinite (open circuit) resistance. Either way it's kinda a moot point, either the meter will show some resistance (good plug), or it'll peg at one end of the scale (bad plug).
That said, the wait light is NOT a good way of determining whether the glow plugs are cycling. My glow plug relay was bad, and although the wait light functioned as it should, the plugs weren't cycling properly.
Hard to start when sitting can be a glow plug problem, or a fuel supply problem. It's my experience that it tends to more often be a glow plug problem, but a leak that allows fuel to drain back to the tank, and then have to be pumped back up could cause similar symptoms. You could try pulling the glow plug card to disable the plugs, and give it a quick shot of starting fluid, and see what happens. If it's a fuel supply problem, it'll most likely start and then die, whereas if it's a glow plug problem, it'll most likely keep running. Whatever you do, DO NOT use starting fluid with the automatic glow plugs working. This also isn't THAT definitive of a test, as the starting fluid may allow it to run long enough at a fast enough speed to move fuel back up, but it's an option.