If you complete the followers of the apocalypse quest where you bug the lucky 38 AFTER you kill or disable Mr.House do they get more information? Or do they just get locked out anyways?

They get locked out anyway, no matter when the quest is done.

http://fallout.wikia.com/wiki/The_Moon_Comes_Over_the_Tower : "This quest will start even if Mr. House is already dead, and will end the exact same way. "