Navarre is an area that has been Basque for large parts of history, but is very much a mixed population today, mostly Spanish-speaking. I don't know when the transition happened so whether it's a recent (like the Italian works programs to de-Germanise Südtirol that Mussolini attempted) or gradual development.
Anyway, yes, Caisse will look like RSH/Bruyneel's Astana from the '09 Giro and Vuelta on the GC, but they've got stage wins already, and let's bear in mind that we would rarely see a Bruyneel team attempt something as audacious as Caisse did in the Tour with Luisle, plus they had no fewer than 5 riders in that break in the L'Aquila stage to the Giro. They're not totally GC-irrelevant with Plaza up in 6th - he claims to be in better form than he was at the Tour - they could have a couple of guys in the top 10 at the end of the race, either by being the next one in after the élites (Tiralongo style), by getting into the right breaks (Deignan style) or by getting some attacking wins and then holding on to their GC position for dear life (Moncoutié style).