Others can comment, but my understanding is that Scrivener only requires Dropbox for syncing to iOS devices. Using other sync services for other synching to other than iOS devices is really up to the user to configure, test, and use. See Using Scrivener with Cloud-Sync Services / Cloud Syncing / Knowledge Base - Literature and Latte Support for a more authoritative position than I can give.
Re other sync services, in 2021 Keith (the Scrivener inventor and guru) commented at ICloud sync in future for iOS - #9 by kewms
Edit: Also see new post PC Windows 10 syncing with iPad using OneDrive - #7 by kewms