Are tail strike landings preferable for an emergency landing on water?
While there probably is an "ideal" attitude to impact water, and it would be nice to crash-land with exactly the correct attitude... it's very much a secondary consideration.

By far the most important thing, when landing on water, is to land slowly. As such, your aim should be to land (/crash) with whatever attitude gives the lowest possible ground speed/descent rate at the point of impact. If that means a "normal" flare, do a normal flare. If that means a harsher flare with a tail strike, do that instead.

The point is that you're in an emergency situation, and your biggest priority is to get the speed right: you likely don't have the luxury of trying to fine-tune your angle of impact and flare. Additionally, you always have the risk of over-flaring and stalling into the water instead, which is a worse end result.

So yes, it may - with some airframes - be beneficial to have a tail strike, but you're far better off just keeping the aircraft under the best control possible and reducing your speed as far as possible