1. How are you planning to combine Morrowind's bloodmoon dlc and Skyrim's dragonborn dlc?
2. How are you planning to combine Morrowind's wampires and werewolfs with Skyrim's?
1: Morrowind and Skyrim are
1: Morrowind and Skyrim are two different games and both the Solstheims are and will be in different world spaces, so the Skywind version is apart from the Dragonborn DLC because 1: different time, 2:Solstheim from Morrowind looked different than the Skyrim one, 3:yeah, they aren't the same, you know were I'm getting...
2: I think werewolves and vampires will look the same as in Skyrim, I don't know if the team will create custom ones, but I don't think so. [I didn't see Jorgen's reaction, yeah he explained it good]
To the best of my knowledge
To the best of my knowledge they're recreating the original Morrowind versions of vampires and werewolves on Skyrim's engine to the best of their abilities, which could in a certain sense be considered combining.
So it really depends on how you'd define that.
Though Solstheim is being completely imported from Bloodmoon rather than Dragonborn. Dragonborn will still be required because of crossbows though.