My grandparents have had a few of these and my parents had one. My parents spent a lot of time trying to get the dogs out to the local sandbar so they could run. The trip there was never very fun but it was a great place for the dogs to let loose.
None of the greyhounds liked getting into the dinghy (it was an inflatable that we pulled right up to the shore, no dock). Once in they tended to go around in fast circles trying to figure out how to sit down and they never fully relaxed.
Only one of the dogs really figured out how to swim and I can tell you it was a huge pain trying to pull it back into the boat when it swam out into the channel and started getting pulled out of the bay. This was an isolated incident though.
I would think that it could work if you have a boat with a big enough area for them to lay down. I don't know how they would react to heeling. Getting them into the boat might be an adventure. The other thing that we learned is you can't take them in a boat where they can see the water through the hull (like a lightweight kevlar or fiberglass boat).