I would expect them to cross-pollinate freely, since they have the same species name:
Tagetes patula.
Also, from the Franchi seed catalog and an online translator, "nana" seems to be Italian for "dwarf" or bush varieties.
I would expect marigolds to cross with bush marigolds. I don;t know which is dominant: normal size or dwarf size. It might be only partially dominant, in which case you might get a whole variety of sizes.
Or the wide variety might not kick in until the second year you let them cross with themselves. Sometimes the F2 hybrid offspring of two inbred F1 plants will all look fairly similar, but the F3 generation might be very varied.
@ZenMan is an expert in Zinnia genetics, but might know about dwarf marigold dominance.
