My Bubba got really matted bad this summer, when for the first time in more than a decade we got invaded by fleas. I ended up cutting out the mats, as they were really under the deepest layer of his hair - and that was in Sept. and it is just really starting to grow again. So be careful if you do shave, it may take time to grow again.
I'm actually sorry I cut his hair, because since then he has gotten a couple bad mats and I have used a great detangler spray (that is also a deodorizer, conditioner) The spray is called Buddy Wash from Cloud Star
www.cloudstar.com
This stuff is great - all natural with herbs and oils. It's amazing how easy the dogs are to brush out with just a couple squirts of this - it also works great to freshen the dogs up between baths (it smells great too - it has lavendar & mint)
The problem with your situation, is you are describing trying to detangle hair at one of the most tender spots on your baby. I know this is an area, I really watch, because my groomer told me once she really had to work on tangles under the legs once - and I thought I had been doing a good job with my grooming, so I was suprised
good luck making your decision on how to proceed