Yes, you're right - a pedigree is a family tree, simply a list of ancestors (for rabbits that must include their varieties and adult weights as well as names or tattoo numbers). The ARBA considers a rabbit purebred when it has at least three generations of ancestors that are all the same breed. But those rabbits can be too big, too small, wrong color, etc., without invalidating the pedigree.
Sometimes breeders use rabbits with breed disqualifications (DQs) for brood stock because they have another characteristic that will improve the herd. A good example of that is using false dwarf brood stock. If they are otherwise good examples of their breed, they can make very nice babies, with the bonus, IMO, of never producing peanuts.
The main negative someone might be concerned with breeding a false dwarf buck to a true dwarf doe would be that the smaller doe might have difficulty delivering larger kits. In my experience, that has never happened. A more common cause I've seen for trouble kindling is that the doe has pinched hindquarters, which is even more risky in breeds that have large, square heads like NDs. So keep an eye on that in your does, no matter which buck you use.
Of course false dwarf x false dwarf will only give you more false dwarfs, so that's out. But I like using a true dwarf buck with false dwarf does because a false dwarf doe is bigger, and can often carry more kits, kindle easier, and feed a larger litter just because she's bigger, as well as eliminating the risk of peanuts. But genetically there is nothing I am aware of that would preclude a false dwarf buck x true dwarf doe combination. If your does are already proven, then you have less worry about kindling trouble.
