The MoTD characters will NOT be coming back. First of all they are not full time Treyarch staff they are actors, yes it is possible that they could hire them for more than one map, but it is one of those maps that is unique, CoTD, it had appearances from actors. In MoTD they were trapped in a time loop and they had to kill the Weasel to break the cycle, (Or the other way round, to continue the cycle) so he is now dead, so to bring them back it just wouldn't make sense, And there is also some strong theorys going around that the original four characters will be coming back in the 4th DLC.
And also another point to make, why would they create a computerised replica of the destroyed world, and then put 4 of the 5 maps in America, that is just plain stupid, and obviously Richtofen is going to be controlling the zombies in DLC 4, and if not Treyarch really have destroyed the story line. So if Richtofen is controlling the zombies in DLC 4, and you are saying the Weasel and friends are coming back, what age would that make them? Think about that.