Is it ok to use pneumatic tools underwater
I do light underwater work as a part of my job. One thing I do is drill in rock underwater with a CP9 rock drill. This is a pneumatic tool but is designed to work both above and under water. It works great as long as it is properly lubed before and disassembled and lubed as soon as possible after the job is done.

I have no first hand experience of other tools, but according to a colleague it is perfectly fine to use more or less any pneumatic tools underwater, he often uses cheap ones and says that they do get the job done.

Edit: I have since I posted this answer used multiple cheap pneumatic tools underwater. I can report that I have had no problems at all in doing so, as long as the tool is disassembled within a day (preferrably ASAP) after being used and lubricated throughout.