Well, since the guy on the website said that they were only selling these as whole busses, not parting them out, combined with the last price I saw of about $3900, it seems a rather expensive way to buy used tires.
But to answer your question, I've never heard of a 'water damaged' tire.
To be perfectly honest, that's why I moved out here to the desert - none of that dodging unexpected puddles and such. It only rains about twice a year here, so during those times (about 20 minutes a time) you can safely move up into the nearby mountains to avoid the possibility of standing water hazards. You can't be too careful with your tires ....