If money wasn't an issue (and you didn't give a F whether or not your quad lived or died....and you had a pit crew that tore the entire bike down every night), I'd give skipping a quad over shallow water a try. For the rest of us that don't enjoy such luxuries, I'd advise against trying it. Not to say that it isn't physically possible.....theoretically it most certainly is....but certain things have to be damn near perfect!!
Sleds do it. Everyone's seen videos of them doing it purposely over a small pond, that usually has a source of warm water dumping into it during the winter so that the ice isn't so thick, and then when you get a few warm days the ice goes away while there is still plenty of snow. Notice how there are always nice flat approaches to the water. But the majority of those videos you see, the guys doing it with their sleds either want to try to kill their sleds or have enough money that if their sled sinks, it's not an issue.
Last year, there was an incident on Sebago in Maine (big big lake, very very deep...like I caught a lake trout in ~150' +/- two summers ago in august....this is the lake that land locked salmon were first discovered and get their name from) involving three snowmobilers traveling from one town, a few miles over the ice, to an event (I think a fishing derby?) in a cove. It's generally very cold in the area so open water is not very common...but the water is VERY deep. Well, these three guys happened to hit open water. Two of them made it to the other side, while one of them was lost. Reports claimed that the two survivors traveled over half a mile over open water!!! They were moving, and once they realized there was open water, they didn't have time to stop, so they pinned it and kept it in a straight line. They un-intentionally crossed more open water than most people intentionally trying to cross open water ever had crossed.
But sleds are (obviously) build a little differently than quads. Sleds are made to slide over (frozen) water....and so they're slightly better suited, should the unfortunate need arise, to skim over water. Smooth flat bottom, wide skis up front, and a trac that would be comparable to a sand paddle, only it lays flat for 2-3'....and it's wider. Plus, with the belt drive CVTs that snowmobiles have, when they're on water and you've got it pinned, there is less resistance on the belt than if you were on solid ground (snow vs. liquid water) so once you get on open water the track must quickly start spinning about as fast as the CVT will allow it to spin!! I wish I could find some articles on the sebago incident....but I'm drunk!
I've never taken a sled over 'open' water, other than some stream/small river crossings....where sometimes you're on ice, sometimes there is ice with water on top, sometimes the ice sinks while you're going, and sometimes your skis are pushing through gravel....but usually you've gotta watch the throttle so you don't roost water everywhere and freeze your ass off!! When there is water over ice, the track likes to spin real quick if you're not careful.
Sorry for the way long rant post....mods, please feel free to delete my un-intelligible rantings.....