I seem to remember Hamilton actually being stuck behind webber for a while. Often falling back through the turbulent air of turn 8 and thus not being close enough on the long straight a few corners later to pass. He was quicker than webber that day for sure.
Drs can be enabled in the wet when inter tyres are being used. Only if the race director deems it safe enough. In suzuka there was a lot of spray at some stages but the actual amount of water on track was safe enough for drs to be used. Obviously these levels changed during the race and drs was disabled at certain points. Hamiltons timing worked out for him here!