YES!
If you want to load from google drive or dropbox, just press the little cloud button in the bottom left of the file picker:
However, you unfortunately can’t use koala’s “ADD LOCATION” to add them as bookmarks because neither Apple nor Google allow third parties to access the files directly like that (iCloud on iOS is an exception and you can add it as a location)
I apologise profusely on behalf of both Apple and Google, that’s all I can do, its literally impossible to make google drive or dropbox more compatible than it is at the moment. If things change I will be sure to update it.