Sadly, the screenshots shoot that theory down, as they depict both the Maid and Butler with Knives and Healing Staffs (or whatever equivalent Hoshido uses). The Maid in particular has the two skills attributed to Awakening's Troubadour (Res +2 and Demoiselle) in her status screen (along with a currently unidentified third skill). Moreover, said maid has 3 Skills and 6 Move at Level 2, which suggests that the Maid Class is a promoted class. I wouldn't be surprised if the same applied to the Butler.
Okay so that would make Maid/Butler the replacement class for War Cleric, at least for Nohr. Do we actually have any details on Ninja beyond that they use hidden weapons?
...and I maintain that maids and butlers stick out slightly less than a ninja would on a battlefield. :p
We know that they're a tier 1 class since our playable Ninjas are this game's Christmas Knights (plus a subscriber to the 'Cecil third wheel' archetype to round out the trio). Other than that, they look to have rounded stats in Str, Skl and Spd, but are going to be made of paper.
Just look at that guy.