We have several Dell monitors and never a problem. However, I'm thinking that the issue is that the computer hibernates before it tells the monitor to put itself into standby mode.
Out computers are set to never hibernate -- Windows really doesn't (in my experience) do that well.
But we do have the power saver settings set to tell the monitors to turn themselves off after half an hour or so.
Maybe you could try setting the monitors to power off at, say, 25 minutes and then setting the computer to hibernate at 30 minutes. Then, when the computer comes out of hibernation, it sends the proper power up signal to the monitor.