Dry ice would push far too much through the tubing, and depending on the diffusion method, either pop something, or possibly destroy the container itself. You would definitely run into problems with too much co2 in the tank as well.
takashi amano was gonna use it when he first started out but he says in his book that it was to hard to control and that the effeiciency of constantly replacing it was not worth it. he then used carbonated water
in the end depending apon how much you put in you would have carbonated water and it would probably raise your acidity to toxic levels. i too have used carbonated water on plated tanks.