The frequency off I1 and I2b in Italy is not necessarily linked to a Germanic presence, many Sardinians belong to haplogroup I, and some of them, in the Middle Ages and the Renaissance, were literally "bought" by the various Italian states for thickening populations of some depressed areas, is therefore likely that many of these stem from the Sardinians in Italy. Anyway I haplogroup is also common in earlier times to the coming of the Indo-Europeans, so it is very likely that only a small part of the frequency of I in Italy belongs to the Germans.
I should add that in Italy to find a Nordic characters is very difficult, the biondismo (blonde hair), although reasonably common, is associated with anthropological mediterranean, or whataver indo-european, characteristics (shape of the face, skin color etc. ..).