Here are some things to consider with pit bulls. First, they can be wonderful, loving pets. They do take an owner who knows what they have. These dogs are highly intelligent and need an outlet. Training, daily walks and constructive play are needed every single day. They need to be socialized at a young age. Your DD's dog has an unknown history, therefore, in my opinion, making him too much of a question mark to bring into a home with children.
Don't assume that the shelter would not have given him to your DD if they didn't think he was safe. They are in the business of finding people to adopt dogs. Plus, they have these dogs in their care under unusual conditions, not home conditions. They also may have had this dog for a short period, therefore not allowing for long term problems to show themselves.
Oh, and as for Rachael Raye owning one - did you know that not too very long ago her dog bit someone? It was all over the news.
I'm not against Pit Bulls. I actually like the breed. But they are not for everyone and I personally don't think they're for families with small children. (Especially an adult with an unkown history.) There are just too many wonderful 'family' type breeds out there that would be a much better (and quite frankly, safer) fit.
I know this is long, but I just have to add one more thought. The reason Pit Bulls have such a terrible rep is many and varied, (some deserved, some not) but I think it has a lot to do with the fact they are a "rip and tear" breed of dog. When most dogs bite, they bite down, release, bite down, release. When Pit Bulls bite, they bite down, hold on and rip away. This causes massive damage to the bite area and is a major contributor to their dangerous nature.