Can I use a dual primary transformer to generate isolated 110v output?
You can if you only need functional isolation.  If safety isolation is required you need a transformer designed for that.

Since you are only powering half the primary you can only put in half of the primary current so you only get half the VA rating of the transformer, so compared to a real isolating transformer you end up with twice as much iron and an unused secondary.


  Safety:
  These units are designed with 4000VAC isolation between the primary and 
  secondary, and also,between each winding and the core. 


If there had been a comma after "winding" it would be a different story, 
as it is there's probably only about 250V isolation between the two secondaries, they may well be wound bifiliar (intermixed)