I�d get insurance before diving with a cheap case   I have no idea what quality that stuff is but a real case is expensive.  Like this: http://splwaterhousings.com/nikon_d200_d300.html

In a previous life, I was a divemaster/instructor with 600+ dives when I stopped logging. As diving deep in deco (I wasn't a PADI diver) puts too much strain on your body in the long run, I stopped it. The last period I was into UW photography, but not digital.

Even when snorkeling (I assume you're not just splashing at the surface, but you'll go down) you need to consider this:
- practice your snorkeling well beforehand in the pool since the key to sharp shots is buoyancy control UW - get a proper lead-belt for that;
- never go down alone; since you'll need to hyperventilate to stay more than 1 min down comfortably postponing the CO2 stimulus, you can faint by lack of O2. You'll need your buddy to throw off the lead belt then and turn you head up at the surface. No kidding.
- don't buy a non-transparent case since you won't see when it's flooding; make sure the O-rings are perfectly clean, especially no sand grains.
- buy a deco balloon. You can fix it to your gear and when you have to let it go, it's easy to find it back at the surface in strong currents and amidst waves. As an alternative, tie the gear loosely at your wrist.
- if you want to shoot some decent stuff, you'll need an UW strobe too since red and orange are gone mostly even at 2m.
- UW photos don't sell in microstock.
- The standard in cases is Ikelite but they don't come cheap.
- If you're splashing at the surface in a (sub)tropical area, wear a t-shirt and pants since without, you can easily get bad burns without noticing it.