There are a few places that recognize the significance of the documentary form even if the writing isn't particularly singled out. The IDA, International Documentary Association is one of them. They have annual awards and offer information and networking to its members. The Film Forum for 24 years has been part of New York's modern art and artifice. Directed by Karen Copper programming its premieres and screening of anywhere from 500 to 1,000 films a year in search of provocative movies for Manhattan's treasured Forum.
Ripples come out in many other places.
In the feature film business the writer either writes on speculation that he will be able to sell his screenplay, or is hired to write or re-write from a producers idea, a book, a short story or even another existing script. Documentary writers can be hired in exactly the same way. There are some writers that have written award winning material and are therefore in demand. I don't think the job search is substantially different in any area of filmmaking. Lots of knocking on doors, submitting samples and sending out resumes.