The zipseal itself is the same whether you are wearing a standard zipseal or a zipglove. The 'zip' portion is exactly the same on either the seals or gloves, so you'd have the same chances of flooding whether you had zipgloves or zipseals.
The Zipgloves are a lot harder to actually install than Zipseals because 1. You need them aligned so the palm is facing the right way, and 2. it's harder to reach inside the sleeve to pop them in place because there isn't a hole through it. I would wager that most leaks caused by zip gloves are because they weren't installed properly, but that's just my educated guess.
I have had gloves flood before. With the atlas (smurf) gloves, the leak is usually a pinhole leak, and I can't even tell until I take the glove off, and the liner is wet. With rings, I just change out the glove, and in 5 min, I'm good to go. With Zipgloves, I would probably find the leak, and dab some aquaseal over it because they cost so much. Compressed Neoprene is even tougher, and I've heard aquaseal works well too. The only catastrophic glove flood I've ever had was when I was wearing a black rubber glove. I was at the tail of the plane in Mermet, and I tried to stop a runaway ascent by grabbing their fin and holding onto the tail of the plane. The metal sliced through the glove, and I had to end the dive.
As far as warmth goes, you need to also balance that with dexterity. I can wear a thick underglove, and have warm hands after an hour in 35* water, but my dexterity goes to pots. I've stopped wearing my heavy undergloves in favor of some army surplus gloves, or a pair of generic polypro work gloves. The work gloves by themselves are fine down to 50*. The wool is a little warmer, but itches, and for the really cold stuff, I still need to decide what I want to do.
Another thing about dexterity is that the outer glove makes a big difference. If I'm wearing a too-big smurf glove that has a lot of extra material, my fingers will slide around inside, and I can't work bolt snaps as well, but go down a size, and with the same liners I gain a little bit of dexterity. I would assume the crushed neoprene adds a little bit of warmth, but does it at the expense of dexterity. From hot stiff the stuff is, I think you would get more warmth with less dexterity loss if you went with smurf gloves with a double liner, but again, that's just my educated guess.
Tom