You can get just about any camera you want, so long as you get an underwater housing.
Housings are super expensive though.
Your lighting will get shitty if you get deep, so you want to make sure your camera can handle low light. A high end camera with its pricey housing might take better pics that a dedicated underwater camera, but you might have to get a second job to afford it. Make sure you get the camera that best fits your needs.
The cameras on your site seem to be cheap point and shoot digitals in a housing, but for a nice price.