Water baths do increase heat transfer slightly and can theoretically keep the tank cooler, requiring less of an over shoot on the fill pressure to achieve the service pressure once the tank cools. But in practice it does not work that well unless the water is moving around the tank as the water next to the tank warms and essentialy insulates the tank from cooler water if there is no flow to carry the warmed water away. Also, slow fill rates are still needed to allow the heat to transfer through the metal, although aluminum is much better at transferring heat than steel.
As for blast reduction, if you filled tanks on the bottom of a swimming pool, you'd have enough water to absorb much of the energy and stop the tank fragments, but the average tank fill trough will not accomplish that.
If you make a cylindrical shaped trough out of 3/8" or better yet, 1/2" walled steel pipe that fairly closely surrounds the tank (a few inches of space all around the tank) and extends well above the tank with only a narrow slot for the hose to attach to the valve, then most of the blast and any fragments would be directed in a narrow cone almost straight up and would not be likely to injure a fill operator. Water in this situation would keep the tank cooler but would have no real effect on reducing the blast other than increase the mass being moved and perhaps reduce the average velocity slightly.
