Re: Dry ice in the ice chamber?
I assume you are talking about putting it in the ice chamber, since putting it in the vase is so stupid I can't imagine anyone trying it.
In the chamber, it would probably 1) cause the hookah to get so cold it might well cause the welds to crack and 2) would let some of the expelled gas into the crack above the chamber, allowing it to get sucked through your bowl.
It's just not worth it. If you want a cold hookah that bad, either freeze an inch of water in the vase before smoking or fill the ice chamber with ice and salt. Either way you'll have an great cooling effect through a full session.
Dry ice is a PITA for any purpose. I had some for halloween and it's just too hard to deal with. You can't touch it, it's hard to keep frozen, it's expensive, and it's hard to find in regular grocery stores. Just the idea of having to break it up to fit into an ice chamber seems like too much work.