You 100% DO NOT need a guide service for the typical Tour du Mont Blanc hike. I did the majority of the tour last year and it's very straightforward.
Here's my trip report from last year: http://www.viewsfromthetop.com/forums/s ... post199949
I can make recommendations for maps, hotels, and for the pros/cons of doing the main vs. alternative routes for the entire length of the loop. PM me for further info!
It's an awesome trip...Enjoy!