The term "syntactic-subject" seems to be referred to in Wikipedia as "dummy subject", and there is a "dummy pronoun". According to Wikipedia, a dummy pronoun cannot be replaced by any noun phrase.
From Wikipedia (There_is),
The word there is used as a pronoun in some sentences, playing the role of a dummy subject, normally of an intransitive verb. The "logical subject" of the verb then appears as a complement after the verb.
The dummy subject takes the number (singular or plural) of the logical subject (complement), hence it takes a plural verb if the complement is plural. In colloquial English, however, the contraction there's is often used where there are would be expected.
From another page (Dummy_pronoun),
A dummy pronoun, also called an expletive pronoun or pleonastic pronoun, is a type of pronoun that adds no meaning but is required by syntax. An example is the "it" in "it is raining".
A dummy pronoun is used when a particular verb argument (or preposition) is nonexistent (it could also be unknown, irrelevant, already understood, or otherwise "not to be spoken of directly"), but when a reference to the argument (a pronoun) is nevertheless syntactically required. For instance, in the phrase, It is obvious that the violence will continue, it is a dummy pronoun, not referring to any agent. Unlike a regular pronoun of English, it cannot be replaced by any noun phrase (except for, rhetorically permitting, something like 'the state of affairs' or 'the fact of the matter'.)
It might also worth noting that (from the Wikipedia's There_is page) sometimes they can be either an adverb or a pronoun, and when it's a pronoun, it's pronounced in its weak form.
Because the word there can also be a deictic adverb (meaning "at/to that place"), a sentence like There is a river could have either of two meanings: "a river exists" (with there as a pronoun), and "a river is in that place" (with there as an adverb). In speech, the adverbial there would be given stress, while the pronoun would not – in fact the pronoun is often pronounced as a weak form, /ðə(r)/.