I think it´s a poor reflection on contemporary trends in political thinking that the statement that nationalism would always trump liberalism, socialism, Christianity or whatever has found no serious opposition in this thread.
A bit of background information on the Saar Referendum of 1935, which has been presented as an argument for the thesis: From 1920 up until 1933, ALL German parties and their Saar filiations had campaigned for the "Join Germany" option. From early 1933 to January 13th, 1935, the parties of the left changed their position and formed an alliance pro Status Quo. Yet, in contrast to the "Deutsche Front", they had next to no means to back their campaign with. Their "mother parties" were forbidden, their leaders and many party members thrown into concentration camps. No external power backed the Status Quo campaign. The Deutsche Front, on the other hand, was massively supported by the Nazis, both financially and, more importantly, psychologically. It was quite clear that if you didn`t fly the Nazi flag out of your window, you could well end up on the deportation list to the concentration camps (the "Angstfahnen" campaign) once the Saar would have joined the Reich. Also, with regards to the Catholicism of your worker: following the Nazi-Vatican Concordate, the bishops supported the Deutsche Front campaign, and I suppose the simple priests followed their lead.
And the anachronism:
Differentiating "nationalism" from "liberalism" in the 1810s is a questionable business. The political Nationalisms of the Germans and Italians were modelled after the French - both in imitation and in rejection at once.
I can indeed imagine, for example, Germany becoming divided between a pro-French (and pro-modern statehood, pro-liberal constitutions) and an anti-French movement, in which case the latter might blend Romanticism more unambiguously with a rejection of modernization, constitutions, mass states etc. The latter would not call itself Nationalist, though, and it would much rather come to identify either with the anti-French monarchies (Prussia, Austria), or with glorified pre-nationalist German entities of the past (primarily the Holy Roman Empire, which isn`t so long dead by that time), or with both. That would be an elitist philosophy, but it could be influential nonetheless.
Nationalism would look very different with a Napoleonic victory. (As would liberalism.)