Immortal pretenders will be ok, however -- also those which are not coldblooded or undead or demonic, such as the Phoenix. Even if they become diseased, they are sure to be cured before it becomes serious. (I tested this and it works well.)
While pretenders can get battle fright I don't think they are affected by it. I have had pretenders with that affliction and they still had morale 30. My guess is this is true for all morale-30 units.
I don't think recuperating pretenders is really a good idea, though. The game doesn't really need SC-pretenders to be better than they already are, and having to deal with afflictions (or pay extra for a regenerating/immortal pretender) is one of the complex challenges of the game.