I don't think so -those are totally different systems. The fob hacking thing is real, but not widely used in the USA AFAIK. The truly paranoid can store their fob in a faraday cage. I just keep the car in the garage. When it's in the parking lot at work, I just count on my insurance to pay up if it disappears. Which I hope it doesn't, as it's a pain finding one of these things, still.
I remember reading a story about how some thieves would steal a Chevy (Corvette, or truck) from a test drive, and the first thing they do is rip out the on-star module. Then they can often drive it for months, years, before they get caught doing something else. So how hard could it be?
I really like the safety factor of having on-star notify EMS if I were to get into an accident. I do not like the fact that they track my every move, and that they want money for that potentially life-saving feature (which was included for free for the first 4 years on my BMWs). So when my trial period is up, I may well be tempted to yank that on-star antenna myself.