I tried to recover all categories having a certain property set, with the API method AssetCategoryPropertyServiceUtil.getCategoryPropertyValues.
The problem is that the results returned by this method are incomplete.
Here is an example of AssetCategoryProperty returned:
We can see that all fields are set to 0, except for the key and value. Which is a bit useless if I cannot get the categoryId!
Do not hesitate to answer should you want me to provide additional information.