I'm using Magic weapon Deflection and Dominance (passive) at the moment but I'm not really sure whether they stack. In other words: Do I get more shields this way, or is one skill just wasted here? Please provide some form of prove with your answer, I'd like to be sure, not to speculate/discuss.
I cannot provide solid evidence myself, but they do stack. If you want to see for yourself all you need to do is hover your mouse over your HP while attacking enemies. This shows how much shield you have accumulated but they over lap very infrequently.
The best way to see this for yourself is to play any difficulty you can kill mobs easily.The shields will be easier to see overlapping due to killing enemies quickly.