Interesting. I was thinking of creating dummy objects to map to object_types a couple of days ago for the same reasons. One bit in the categories admin UI shows all packages that are "using" a category tree, but otherwise it should work. I have sucessfully mapped category trees to content folders and checked on that mapping to see what category trees were valid.
The best solution long term is to make object_types objects themselves.
Thanks for the heads up. You're probably right, that making types objects is better, but what type would the first one be? In other words, when you type that a type is an object_type, would the object have type type? :)