I know of several guys who study tea ceremony. Can't say as I know any who study ikebana though. There are plenty of guys who study kyudo though (archery).
I don't think there are any rules. For tea-ceremony (sado) and ikebana there tends to be more girls who actively participate and this may have to do with the fact that they were traditionally taught to girls as home-making skills but I don't think you can make those generalizations anymore.