Well, it worked but led the way to the next problem:
The UIbutton script now registers the Press command (changes color) after the GenericEventHandler was added.
I added a UIEvent Trigger to the button so I could have OnRelease notify but it nothing happens (the UIButton's OnClick does nothing either). Interestingly, I am getting my desired functionality with OnDragOut (mouse down over a non NGUI object, button pops up, drag mouse over then drag mouse off) but I can't get it to register an OnClick or OnRelease.
Any ideas?