After looking at some New York Times references on the internet, I think this is just another word for "fellow word-lovers". Here's one example of the word being used in the paper to refer to people who are collecting unusual statements made by Ben Bernanke: http://schott.blogs.nytimes.com/2009/08/03/when-the-co-vocabularist-comments/ Here's the quote: A brave band of co-vocabularists took up the challenge of creating Bernankisms fit for our times.
It's an example of the language evolving even when you wish it wouldn't. Strictly speaking, I suspect it's the invention of a new word when a perfectly good one (lexicographer) exists already, but I also suspect the intention is to contrast the focus on thinking up new words (vocabularist) with that of compiling others' inventions into a dictionary (lexicographer).
Presumably those interested in thinking up new words couldn't rest easy unless they invented their own label.
I think we are misunderestimating the truthiness of the neologogenesis of these vocabularists (and their co-conspirators, oops -vocabularists). Perhaps they might better be described as neolexicographers, charting words well before they enter the territory of conventional lexicographers who only consider words that have been around for a few months or years (?).