I don't see a space in the IC2 API to add custom recipe scanning to the UU system... but if there was one I'm sure some mods would add UU-support (or at least compatability addons). I mean like, an ArrayList of IUURecipeHandler or something like that, and a couple of public methods to manipulate the graph. Maybe it is already in there and I am blind, but from Eclipse's Class File Editor it looks like UU is an internal thing.
Yes the api is currently internal since I'm not fully convinced of it, you can find it in ic2.core.uu (IRecipeResolver, ILateRecipeResolver, RecipeTransformation).