In addition to hound waves not occuring when you're on a boat, when you do get a hound wave, the hounds face two issues. The first is that they sometimes have trouble getting into the ocean for some reason, and just seem to run up against the land. Gif here as proof:
The second problem is that when hounds enter the water, they're not given the wetness prefix. This is evident by the fact that it took two electric darts to kill a hound (150 hp - 90 damage - 90 damage = 2 elec darts) rather than one electric dart (150 hp -150 damage = 1 elec dart). Gif here as proof:
I used a panflute against the hound wave to make them sleep so that this test could be done.
Steps to Reproduce
Case one. Put dogs to sleep. Go out into water. See that dogs, although agroed on you, don't jump into the water for some reason. Case two. Get a dog in water. Use electric darts. See that dog didn't die in one shot.
This issue has not been confirmed by a developer yet.