grammaticality - Is "Are" always used with plural verbs/nouns?

Yes, it should be "there're". I suspect that speech has a role in the tendency to substitute "there's" for "there're" because the contraction "there're" is nearly impossible to pronounce clearly. I've heard people use the both contraction "there's" in speech in one instance, and a few moments later, while referring to the same event, use "there are" if full form. I've also witnessed someone testing out a sentence by speaking it, and using "there's", and using the correct contraction when the sentence is written.