Just a data point... This website: http://www.smokers-united.com/index.php?ln=en#
defines "smoker-friendly hotels" as hotels with "smoker rooms" OR "rooms with a balcony/terrace" and lists the ratio as follows:

Hotels with smoking rooms: 24492
Total smoking-friendly hotels (Rooms with balcony/patio): 88178

Clearly, a great number of hotels allow balcony smoking in nonsmoking rooms.