Well here is the thing. The ram is always covered on the GT and Ultra cards from nvidia. But ATI uses the same exact RAM running at the same speeds and they dont cool the ram. I think nvidia just decided to cover the ram up to make sure it wont overheat in any circumstance as well as make it a bit better for OCing.
but it isnt neccesary. With the water cooling the gpu will be pretty cool compared to stock so u wont need the ram coolers. When the system has the ramcoolers attached to the gpu cooler the gpu would (i think) actually put some heat into the ram. With that disconnected the gpu wouldnt be heating up the ram any more.
Further proof. Xbitlabs did a review of hte 6800 ultra where they put a water cooler on the card and they didnt use any ramsinks and they actually got an improved RAM overclock compared to stock and some really good ocing on the gpu it self. check it out at
www.xbitlabs.com Its in the graphics section.