After a lot of messing around with various settings in Drupal 5.0 I found that in order to edit your site with an external client such as Ecto or docs.google.com you have to turn on the blog entry content type and then give the user access to “edit own blog”. I guess I hadn’t tried to connect without having the blog module turned on even though the blogapi module lets you access other content types.
I currently use a custom blog content type, which I could continue to use, but I noticed something once I turned on the blog module. I pull in feeds for my del.icio.us tags and Google Reader starred items, and now there’s a small link next to each feed item that lets you click on that to start a blog entry using that item’s information. I just checked it out, and I don’t know how useful it will be since it uses the existing item’s title as the new blog entries title and the body of the entry becomes the link to the item. It might turn out to be useful in some way though, so I’ll switch to using the blog entry content type and keep using the /articles path for the blog entries.