Well... theres no real strategy guide on how to play them. However, there is:
LA Atlantis, another thread looking for tips
Seal Hunters are by no means great, but they're strong for chaff- don't underestimate them. Harpoons may be useless underwater. Go figure. Not sure.
Their water mages aren't very special- Mictlan and Patala, for instance, have W3 mages as well. Still, its easy enough to get Angakok to W5 or W7 if the random picks are right.