Playing with the tool some more, I can see that Andrzej is right.  
There are a number of missing features in the polygon tool that exist 
in the zone editor.  Adding corners is a large one.
If you have an existing non-copper zone, it seems you can keep it, 
change its layer, add cut-outs, etc.  Even duplicate to create a new 
one.  But you can't draw a brand new one.
-S
2018-02-23 17:07 GMT-08:00 Andrzej Wolski <awolski.kicad@xxxxxxxxx 
<mailto:awolski.kicad@xxxxxxxxx>>:
        Was it ever possible to run the fill algorithm (meaning, only
        fill in parts of a polygon outline, based on some clearance to
        other items on the same layer) on a non-copper zone?
    No, I didn't mean it was already possible.
        Seth, yes I see that dialog too in old builds, but the outline
        appearance doesn't do anything (because non-copper zones are
        always shown filled, not with an outline)
    Zones on paste layer shown in outline::
    https://imgur.com/a/5g4cI
    Andrzej