I usually don't answer my own question, but in this case I have to I guess.
I am running Minecraft pre-release 12w36a and I can confirm that you can cure infected villagers spawned from dungeon zombie spawners in survival mode.
I had a zombie spawner underneath my base that I never destroyed, I am glad I kept it. I set up a small killing device for killing the unwanted zombies, and waited for a infected villager. In my case it spawned one every 30 zombies or so.
When I got one I used a splash potion of weakness (water bottle + fermented spider eye + gunpowder). As soon as I threw it I got my golden apple in my hand, and just right-clicked the villager. At this point he started shaking.
While he was shaking, I waited around. About 5 minutes later he turned into a normal villager.
At this point I wanted to know if he would despawn, so I went exploring in my world, slept for a few days, and went to the nether a few times. When I came back he was still standing there, which was great.
I do not know if this will stay in the game. I will update the game once in a while to see if it still works in the snapshots.
For now I will work on setting up my village, I am glad I don't have to build the 1000+ block railway anymore.
I can confirm this works in 1.4.2, see the video in the question for more details.