No, I think you are right. Homebuilt ultralights are rather rare down here - actually I am unsure whether they'd be registered as ultralights OO-[A-Z][0-9][0-9] or rather as experimentals OO-[0-9][0-9][0-9]. It might well be there is no official category dedicated to them, so that their builders have no option but to register them as generic "ultralights". Anyway, the "permit to fly" document for both categories is under the hands of one and the same person.