Ice doesn't work like that i'm afraid, Tanks will still sink even if really shallow water (Ice mechanics). And i don't have any other clue how to make water look like "ice", any ideas anyone?
Well actually relic uses "shallow ice" in a few map to offer safe crossings, ex: Pripyat Winter, here's a video example were two kts are on a frozen lake one has shallow water beneath it and the other one has deep water beneath it. if there is any deep water beneath a unit it will sink when the ice cracks.