Not only is disc golf a great way for an obese person to begin exercise, it can also be a catalyst to make them look for ways to exercise more.
When I began playing, I was missing shots because I would be out of breath by the time I would get towards the end of the round. The person I had become was holding me back from what I wanted to be. However, I was a couch potato and working out just to lose weight didn't ever work for me.
I remembered from playing football and baseball in high school that if I had something to train for then I wasn't exercising. This may sound silly to some people, but this was what motivated me to do something about my obesity. My health wasn't measured by a scale but by the distance I gained on the field and the accuracy I picked up by putting. My trophies, just like in the days of playing football, were the sweat drenched shirts I had at the end of practice. I've now motivated my wife to come out and join me as well in disc golf practice.
So I believe that not only is disc golf a great way to exercise in and of itself, as has already been pointed out, but I also believe that disc golf can motivate individuals to exercise more off the course as well. It gives them something to focus on that isn't a scale telling them that they aren't doing enough.