Solid answer for what? There's no rule against using sprites. As long as you don't like make a animated splash GIF to create the entire effect.
I was going to enter, and could have easily pulled out a nice slash effect using sprites but I failed to be able to get hold of a solid answer on the subject and therefore, gave up.
Seriously, if you can easily code a nice splash effect, why not enter?
But that's the whole point of a coding challenge: to figure out ways to accomplish something. If everyone already knew how to do it... it wouldn't be much of a challenge.
I don't think splashes is the best theme to get a lot of people participating - because I for one, expect that if I entered, my entry would easily be eclipsed by people that are familiar with getting ripples to work correctly.