the problem precisely is that if you assume that there is an underlying structure noun is raining object then from the very start you deny the possibility that the pronoun before the verb is in fact meaningless i e a dummy word if the pronoun refers to a noun and you can say what this noun is then by definition it's not a dummy pronoun my contention is that maybe the verb is really impersonal i e its subject is truly a dummy word not meant to mean anything but only appearing there to fill a syntactic slot the definition given at the start of the article is not sourced appropriately i know it just covers what i think are the features of what linguists call dummy pronoun based on my amateur experience on the matter i know it's not completely wrong or misleading though it probably needs a different form the glossary definition above otoh is a bit too vague but in any case note that the very first example of dummy word given below in the source is the it in it is raining