Do Burrowed Units Block Building Construction?
Yes, it does block construction and landing. Confusingly to the other player, it will show the building in all green when they go to place or land it, but upon trying to actually land or build, will be unable to.
Yes, it does. My 2v2 partner and I have won games several times against unsuspecting people who never realized that we burrowed one innocuous zergling under each of their possible expansions. Been accused of hacking.