Ah, but does Dawnguard glitch the alchemy lab for your Hearthfire home, too? As it stands now, with Dawnguard installed, I can buy alchemy labs for Breezehome eternally without it ever being delivered.

That glitch only applies to Breezehome it doesn't apply to any other house. (DLC also can't directly interact with one another). So even if the glitch affected all houses it wouldn't effect Hearthfire as it will use different scripts for building and furnishing the house.

Why do you say that? Do you realise that patches are also DLC? The features from recent patches are inteacting with DLC like Dawnguard. I bet that Hearthfire will also allow you to recruit followers from Dawnguard to use as Stewards in Hearthfire, not to mention being able to smith Dawnguard items in your Hearthfire home. The only reason why certain DLC looks like they dont interact, is because it reduces the dependencies and makes programming easier. However, there is no physical reason why DLC cannot interact with each other.