There are two different uses of the word "customer" here, with emphases on different parts of a particular kind of transaction. (And both are "legitimate" -- that is, they are in broad use in English.)
(1) "PURCHASER" of a good or service, as opposed to SELLER.
(2) "CONSUMER" of something, as opposed to PRODUCER.
In the first sense, of course we don't have customers, we're volunteers.
In the second sense, Google is an ODP "customer" (licensee), and so, of course, are surfers who get information directly from dmoz.org. And so are any other website proprietors who download the ODP RDF and publish it on their own website. (But that is the only service the ODP provides to website owners, in any sense.)
Editors are volunteers, but so are people who make constructive suggestions to the site, by all the various mechanisms set up: site suggestions, update listings, abuse reports, quality feedback. And in neither sense (and in no possible way) are volunteers "customers" of each other.
That's worth emphasizing: none of these are ways of requesting service, they are all ways of freely offering service. Using them to demand service is abuse, pure and simple.