The Foundry Nuke hack works with "nukescripts.panels.registerWidgetAsPanel", to remove the disturbing widget contents margins set by Nuke.

setNukeZeroMarginsWidget.py

'''
Created on Feb 8, 2013

@author: matthieuc
@contact: matthieu.cadet@gmail.com
'''

import PySide.QtGui as QtGui

def setNukeZeroMarginsWidget(widget_object):
    try:
        if widget_object:
            target_widgets = set()
            target_widgets.add(widget_object.parentWidget().parentWidget())
            target_widgets.add(widget_object.parentWidget().parentWidget().parentWidget().parentWidget())

            for widget_layout in target_widgets:
                widget_layout.layout().setContentsMargins(0, 0, 0, 0)
    except:
        pass

I've updated the code, I think it is better to not parse all the application Widget with QtGui.QApplication.allWidgets()