Yes, it belongs to a special "Zero-argument" class of verb.
Normally predicates take 1, 2, or 3 arguments;
respectively, these are called Intransitive, Transitive, and Bitransitive:
- Bill arrived. ARRIVE (BILL) Subject only
- Sarah greeted Bill. GREET (SARAH, BILL) Subject and Direct Object
- Bill gave Sarah a gift. GIVE (BILL, GIFT, SARAH) Subject, Direct and Indirect Objects
But not all predicates have arguments. This is rare, but weather predicates are a case in point. Weather just happens, and nothing is implicated culturally in its occurrence, beside the event itself.
- It's raining. RAIN () Dummy it subject.
The dummy subject here is called "Weather it", to distinguish it from the "Distance it" of
- It's a long way to Tipperary.
and the "Extraposition it" of
- It's difficult for me to understand this.
In languages that aren't as fussy about subjects as English, the verb rain by itself (suitably inflected if necessary) is a complete sentence. In Indonesian, hujan means 'rain', both verb and noun, and "Hujan!" is an ordinary sentence that means, unsurprisingly, 'It's raining!'. Just like the English utterance "Rain!".