Yes, you can make a 16mm lens out of a 35- but there are some limitations. This is from using the Sea & Sea SWL16.
The minimum aperture changes from f2.5 to f5.6. The second limitation is focus. At f22, everything from 1ft (.3M) to infinity is in focus. But if you open up to f8 it is more like .8 meters to infinity. F11 is something like .6 meters. So, if you want to get close, you must stop the lens down. To keep the backround water from darkening you will need to adjust the shutters speed to 1/60 or 1/30.
My experience was with slide film. A few of the photos were spectacular. Many were a little soft because the subject was too close. It was during my early days, so I didn't really think to slow the shutter to 1/30 or even 1/15. You can always use 200 or 400 speed print film and set the lens to f16. I'll see if I can dig up an old image to attach.
Two things to remember:
1) It has to be attached underwater. Water is necessary for it to focus.
2) Set the Nikonos 35mm lens to infinity
If you can find the lens cheap, go for it! This type of lens is very popular for digital cameras because those cameras allow for closer focusing. But for the Nikonos, it was indeed a poor man's 15mm.
I would also encourage you to look for a used 15mm or 20mm lens. The 20mm can be bought for about $300-$400 with viewfinder on eBay.