I don't agree, CK. seems to me that the PP in this case is "of the men who do the work"... it's an adjectival clause modifying "one". similarly, "who do the work" modifies "men".

The verb MUST agree with its subject, not the noun in a PP.

yes, and in this case the verb (is) is indeed in agreement with the subject.... "He is one."

would not the sentence, in diagram form, show "men who do the work" as the prepositional object, with "who do the work" as the participle phrase modifying the noun "men"?