I remember there being an IFTTT recipe for syncing DB and Google Drive, but I never gave it a try. I was using DB before I used Drive so I'm fine with Orgzly's reliance on it, but there are options.
I use syncthing to sync Org content between android and linux for orgzly consumption. I don't see any reason why I couldn't add a syncthing that copied into a mounted Google Drive if I wanted my info up on that cloud.
Too invested in the Google ecosystem to also depend on Dropbox.
I have tried some folder sync apps, but I prefer not to depend on those either.