Thank you. Unfortunately, the only way to use the Caballeros card with the Germans is to get lucky and get the Elmetti as a mercenary unit on the map, plus it would be wise to send the Mercenary Camps card + Improved Mercenaries.
PS: I would love to see the 7 Elmetti card enable them to be trained, from the bars and camps.
My knowledge of German civilization is limited, but you might want to approach this the traditional way, focus on cavalry and outmaneuver your opponents with a food-based mono-economy.
But if you’re interested in using a less conventional strategy, I could technically have guard-level Saxon Cuirassier and Totenkopf Hussar at a 45% discount thanks to the city cards.
My recommendation would be to make two decks, one for when you have access to Elmetti and another when you have access to several House of Wettin and Hanover, but I leave it up to you which strategy suits you best.
PS: In theory, the Germans have the best economic recovery for the Argentine revolution thanks to the Mills boom. I suppose that what they lose on one side they gain on the other. 
Note: I recommend that you see this guide, you may find it useful and who knows you may even end up creating your own strategy. 
Crazy idea, that the developers give Argentina access to Elmetto, Royal Horseman and Mounted Rifleman, along with a -1 population reduction for the Royal Horseman and Mounted Rifleman.