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: [email protected]
'''

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

First of all thanks to maty974 for the original code-snippet.
It didn't work out of the box for me as well but I ultimately got it going.

def setNukeZeroMarginsWidget(widget_object):

parentApp = QtGui.QApplication.allWidgets()    
parentWidgetList = []
for parent in parentApp:
    for child in parent.children():
        if widget_object.__class__.__name__ == child.__class__.__name__:
            parentWidgetList.append(parent.parentWidget())
            parentWidgetList.append(parent.parentWidget().parentWidget())
            parentWidgetList.append(parent.parentWidget().parentWidget().parentWidget())

            for sub in parentWidgetList:
                    for tinychild in sub.children():
                        try:
                            tinychild.setContentsMargins(0, 0, 0, 0)
                        except:
                            pass

Because setNukeZeroMarginsWidget was wrapped in a try/except block the function would exit as soon as it encountered an issue. In my case, one of the children of one of the widgets in parentWidgetList was a QObject, so it didn't have a setContentsMargins method. This caused the entire function to exit prematurely before setContentsMargins could be executed on the desired widgets.
By moving the try/except block further down the line we can still prevent the function from failing should we attempt to setContentsMargins on objects which don't allow that, however it won't exit prematurely any more.

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