I've no real experience of putting up antennas on the chimney of a house.

I have seen chimeys come down in severe wx with just large TV antennas on
them. I guess it would be dependent not only on the structural integrity of
the chimney but also physical size but I certainly would be careful. I
don't know your particulars but wouldn't it be better to have something
bolted on the side of the house even with the insurance issues????

Good Luck and God Bless Tom KI3R