To answer the question in the title, nothing can certainly be preceded by a plural verb. We should distinguish two types of situations where this might occur; one is much more clear-cut than the other.
Sentences where "nothing" is not the subject of the verb, so the verb agrees with another noun phrase that could be plural
Noun phrases linked by the verb "to be" are not treated equally in English: only one can play the role of the subject. The other is merely a "complement" or "predicative noun". The verb "to be" agrees in number with its subject, not with its complement, so regardless of whether nothing is singular or plural, only plural agreement is appropriate in
They are nothing but petty thieves
because nothing here is only the complement of the verb (or if you prefer, of the subject); the subject of the sentence is they, which is indisputably plural.
As you say, it's clear to anyone that "They is nothing but petty thieves" would be wrong. So in fact, in this circumstance, nothing actually HAS to be preceded by a plural verb. It could also be preceded by a plural verb if it takes the role of grammatical object (this is probably also obvious after being pointed out): we have to say They ate nothing, using the plural verb "ate" to agree with the plural subject "they".
Sentences where "nothing" is the subject, but maybe would take plural agreement
There are nothing but liars in here.
A "There are..." sentence like this is a more complicated matter. Despite the surface similarity, it doesn't necessarily have the same structure as a sentence starting with "They are...". Traditionally, the there of the existential construction is NOT taken to be the subject of the clause; instead the following noun phrase is the subject (which is why we normally select "there is" or "there are" based on the number of the following noun phrase).
In a situation like this, the grammatical number of nothing is indeed relevant. There's another question specifically about this issue: Is “nothing but birds and a few insects” singular or plural?