At the moment you can limit 'nades, but not specify which type. In my opinion smoke is a real issue on public servers, sometimes there's so much of it the game becomes unplayable.
I don't really want to get into a discussion on whether smoke is good or bad, but it appears to me the community is kinda polarised on the issue. I see lots of people complaining about smoke, but also lots of people using it. Personally I leave servers if they become too smokey, but I know people who couldn't
If there was an option for server admins to specify which type of 'nade to restrict I'm sure we'd see many smoke-free servers appearing, which I and others could enjoy leaving the smokers to knock themselves out on normal servers. That way everyone's happy.