I don't think that he's necessarily invoking the extreme reactionary past that you speak of, more the generic conservative Catholic one. De Maistre would have found the idea of the Republic as an organic heir to two millenia of Christianity to be positively obscene, not to mention utterly absurd. But it is a clin d'oeuil to the traditionalist conservatives who form a part of the Le Pen vote and pretty much all of the de Villiers one. And while the UDF has in recent decades been the more centrist right wing party, it was originally formed out of a catch-all broad alliance of non-left, non-Gaullist parties - from just left of center Christian Democrats to remnants of the old right which never could completely forgive de Gaulle for his immediate rejection of the National Revolution and embrace of the Republic. For all I know some of those might still vote UDF out of some atavistic instinct.