The point about France and the Confederacy applies to the period before France was defeated in the Franco-Prussian War; after this, people started copying Prussian/German uniforms (can't win a war without the Pickelhaube), and also, the result of the war in France was the end of the Second Empire and the establishment of the ... Third? Republic.
The Third Republic would be more friendly to the Union, I would suspect, than to the Confederacy. On the other hand, the Prussians might well decide that the Confederacy was a convenient ally, especially if the French were allied with the union.
Of course, in your timeline, France (due to the advantage of its superior warmachines, designed by Monsieur Verne), might have beaten the Prussians anyway (as suggested by Plynkes in
this thread here).
There is a Confederate force on Atlantis, by the way - it was operating in the east and I think V_Lazy_Dragon and Whiskeyrat were using it (and some Prussians) - as outlined on
this part (page 9) of the main thread.