Should isolated GND be tied to logic GND to prevent ground drift?
Is this, in reality, what happens?


No, this is usually not what happens because for a static charge to build up, the isolated circuit would need to be isolated from all objects with materials that are high resistance/large dielectric breakdown. Most isolated circuits are tied to ground on both ends and the isolation is to prevent ground currents/ground loops.

It is possible to get a static buildup, but the circuit would need to be isolated from everything, and have a charging mechanism. 

In space (vacuum) this is actually a problem, and isolated conductors can develop a charge (from radiation) and cause breakdown. On earth not so much because most objects are connected to ground in some manner (even if it is high impedance). 


  What is the proper way to address this? I have heard someone mention
  using a 1M resistor to tie isolated GND's to primary logic GND to
  prevent drift -- does this not violate the benefits of the isolation
  in any way?


Tie both ends of the circuit to their local ground if possible, don't tie them at the point of isolation. Or provide a reasonably high impedance pathway (like a 1MΩ resistor) to bleed off charge. Take care if the isolated system is also providing power isolation (like 440V).  

I'm willing to bet that both sides of the system are already tied to ground in some manner (unless you have isolated power also for the isolated portion).