Ok, I had no serious intention of trying this. But I got invited to a quickie UB run to help out a guildie yesterday, so I thought "why not?". I mean, I was there and all. Unfortunately I wasn't able to stick around after we cleared, I had errands to run. But I camped inside the instance hoping I'd be able to pop in later and wander at my leisure. Sadly, this didn't work. The whole place had respawned when I got back a few hours later <grr>. But luckily Kali was able to sneak around and find a spot near the water where she wouldn't aggro any mobs.
And the verdict? Not worth it.
The same exact fish spawn here that you can find in Zangarmarsh. I got Barbed Gill Trout, Feltail and Sporefish. Why would anyone bother coming here to fish when they can just fish outside? No clue. Perhaps someone else knows something I don't, but I see no reason why Blizzard devoted actual Dev time to adding this "feature".