Why won't my Airport Extreme mount my USB 3.0 External Hard Drive?
Per Thermaltake support:


  The Airport Extreme Base Station cannot provide the proper driver support for the docking unit. The docking station was designed to be directly connected to a computer's USB port. 


Not a very satisfactory answer, but I guess it is the answer.  I expected it to simply function as USB 2.0 speeds, rather than not working at all.