The definition of Nation is not the same as State. State is related to power+land, while Nation is related to people (ethnically speaking)+power+a certain land (the land of the forefathers, the Promissed Land, whatever). So, if the Lebanese Xiites consider that land as their own, and if Hezbollah can rule that part of the country as a "Xiite country", than Hezbollah is a nation.
Nevertheless Hezbollah possesses all the elements of State power:
1 - an army (wich is far more powerfull than the official lebanese army);
2 - a diplomacy of its own with foreign powers;
3 - media facilities (whose atempted closure trigered the latest events in Lebanon) which equals to more power;
4 - economic means to bolster its activities. They don't have to produce, like Israel, they receive instead.
So, that's the problem I referred to in the first place: how to deal with a quasi-State entity such as Hezbollah which, even if it doesn't intend to invade Israel, it still carries attacks beyond the borders, receives support by foreign powers and is, in fact, more powerfull than the Lebanese State itself?