I would be inclined to think that "yes", excess water can dry out his pads over time. I don't get the "zinc stuff" you mentioned, , but I found out how much Tuf Foot costs.
http://www.tuffoot.com/order/index.htm.

Of course, his recent injury will have to heal some, so, I'd try the " boot camp" method , Neosporin /gauze, , then, try to stay ahead of the dry pad problem with specific moisturizers, or, balms.

I had a Dalmation who would injury his pads, but , he never ripped them open!!!