Yes; I imagine largely because the braking surface is less likely to get a regular soaking from passing through standing water.
That aside I've not actually ridden my current disk-braked bikes in really heavy rain to get a really good idea of how they behave in such circumstances; but I'd expect it to be better due to the holey nature of the disks allowing water to clear easier as well as the higher clamping forces available and different materials used.
Hopefully I'll find out first hand eventually!
