In Summary:
Both UIFigures and Figures are matlab.ui.Figure and so both use the defaults defined similar to
set(groot, 'defaultFigureUnits', 'normalized')
However there seems to be a bug and UIFigures are not currently use these defaults and a ticket has been submitted.
The new ui comonents like uilabel (which is a matlab.ui.label) do not have a units property like the uicontrol('style', 'text') do.
When setting defaults, use
class(uilabel)
class(uifigure)
to figure out the class name for use in the set(groot) command