Dock is just like before - activated by the magnet housed in the dock itself and the sensor built into the phone. If you cover is too thick for the magnet to activate the sensor, or to allow for proper alignment to allow for activation, then it will not work.
Those with silicon covers should be able to press more firmly, but with non-flexible materials like hard plastic, you may just be out of luck.
I bought the shell holster combination and it doesn't seem to work - but I forgot to try without the insert....