I wrote the canadian DAT a few weeks ago, which requires a soap carving. Let me tell you that I sucked when I first started, and had no real training of my manual dexterity except for maybe a few video games (okay lots of video games 😀). After carving about 15 soaps, it become easy as pie and I could carve them accurately at a pretty fast pace (in the cDAT you need to look at the model, measure your soap, make your lines on the soap, and then carve - all within 30 minutes).
So I think that if you have descent manual dexterity to start out with (which almost everybody does) and you practise a hell of a lot you will get good at it.