I have a flat top...which I hate...but I use my cast iron skillet, dutch oven, and grill/griddle on it and I have no problems...BUT take care to not just throw it down on the glass top as is easy to do with heavy pans like that. I have heard of the glass top cracking before due to carelessness with cast iron. Use it and enjoy!!
I use them.I don't see that hey are prone to scratching any more than any other pan.
It works best if it has a flat bottom. Some have a ring on the bottom, so they don't make great contact with the stove top.
I hate my glass top stove. If I replace it with an electric stove, I will get the old fashilned kind with circular burnere