As someone that works for a large game company, I can tell you immediately that if you claim to already have XDK experience, but didn't have a license and didn't work for an official Xbox developer, most companies would not come near you with a ten foot pole. You could possibly be considered "tainted", much like anyone that claims to have had the leaked Windows source from a few months back. The company will not want to risk hiring you and then being responsible for your illegal use of the XDK (as they will be, because most game development and software development house contracts specify that anything you create while hired, whether at work or at home, between work hours or not, is instantly their property).
Also, it shows that you're willing to break the law and go through illegal means to do what you want. What's stopping you from doing the same with the company's games or source code?