When I posted about this the other day, I hadn’t received a reply from Wilson yet. I have now, & here’s the crux of their reply:

Library Literature & Information Science (like the other H.W. Wilson databases) indexes the contents of its journal list cover-to-cover. In practical terms, that means that any article of a least half-a-page in length will be indexed.

The issue of who retains copyright to the article has no bearing on whether the article is indexed or not. It only determines whether Library Literature can provide full-text access to the article. We host the full-text of articles only when we have received permission from the copyright holder. Assuming your publisher has a full-text agreement with H.W. Wilson, your retention of copyright would prevent the article’s full-text from appearing on WilsonWeb.

This is pretty much the same as CSA’s reply. I don’t have any more information than I had before, but at least I don’t have to worry about my in press article getting indexed in the databases I want it in. But the issue remains, the publisher has a statement on their site that material “will be submitted to third-party database aggregators”. What aggregators are they referring to? My next step here will be to contact the publisher and find out about that.