1. Create a mod, which depends on an existing Workshop mod.
2. Publish your mod to the Workshop, and download it to your games mods folder.
3. Make some observable changes to a locally loaded resource from your mod (so not a world, which would have entities streamed from the server), like e. g. modifying a material.
4. Run the Dedicated Server Tool, using this as params for both server and peer client:

-addonsDir "PathToProjectsFolder,PathToDownloadedModsFolder"

Both paths need to be specified, because the application needs to find both the edited project and the downloaded dependency from your mods folder.

5. The game will appear to start correctly, but it is possible you will not be able to observe these changes on the client side, because the client loaded the downloaded version of your mod from PathToDownloadedModsFolder, instead of the editable version from PathToProjectsFolder (like the server application correctly did).

The solution for this would be to make the applications consistently load addons, by first looking in the first specified path, and only loading something from the second path if the addon was not found in the first one.
Right now, the only workaround for this very annoying issue is to not specify your PathToDownloadedModsFolder at all, and instead copy downloaded dependencies to your projects folder.
However, this workaround is extremely inefficient, since you have to manually re-copy things whenever any mod you are using as a dependency is updated, so I'm hoping for an actual fix.