The reason I ask this is because I was going to get an underwater disposable camera to take on my next trip, but I've heard that the X-ray machines that they have at many airports will mess up your film. If that's the case then I might just have to part with some money to get an underwater digital camera.

The security at the Aruba Airport is relatively lax ... but they probably would catch a digital camera on an X-ray. If you're polite and explain the tourist thing they probably will let it pass after checking it.