What kind if medium are you talking about? The desktop applicaiton isn’t aware of the cloud storage behind. If there is an sync client for the cloud, Cryptomator can be used.
On mobile devices it is a bit different, we have to use the API of the cloud providers (at the moment supported: Dropbox, Google drive and OneDrive) or they support WebDAV (WebDAV URLs of Common Cloud Storage Services) which is also already implemented.
P.S.: According to their site, WebDAV isn’t available for SpiderOak https://support.spideroak.com/hc/en-us/articles/115002733483-WebDAV