As long as you don't do it up too tight, you can get away with a UNC screw in a Whitworth thread but eventually it will wear more than the proper mating threads.

When I looked into this a while ago I found one tripod manufacturer who specified UNC and another using Whitworth so there doesn't appear to be a standard.

Likewise, there is probably not a standard with cameras but I suspect that German and Japanese manufacturers are using Whitworth as that's what they were using before UNC existed.