The same seed should absolutely generate the same dungeon. It's what I used for testing, even. That's all it affects--the generation of maps and their contents throughout the game.
And... wow, I just went to test it and it didn't work. Well damn, no idea how that happened since it was working perfectly not long ago.
Moving this to bugs and will solve.
Edit: It was likely some last minute changes to the seeding system that I made while working on the trailer (I was using some hacks to force a specific map to generate repeatedly regardless of other conditions or seeds).