OK, does Dragonborn contain new stuff that will be un-obtainable without Dawnguard? Will Dragonborn add new for example crossbows that those without Dawnguard will miss out on, even though it was Dragonborn that added those hypothetical new items?
I see what you're asking.
For example - Dawnguard adds the Crossbow animations/mechanics.
Therefore, does Dragonborn require DG to use any crossbows you obtain in Dragonborn, since the animation was added in via DG.
That is a very good question actually...