Do electret microphones have polarity?
Yes, they have polarity and it has to be right to work- the output needs to be biased positive with respect to the ground terminal. 

The ground/GND terminal should be common with the case, so you can check polarity with a multimeter. 

Here, from a Panasonic Datasheet, is a typical arrangement:



The two diagrams you show are equivalent, one is just drawn upside-down (potentially.. as it were.. confusing and not to be encouraged, but still valid).