That's more a question for the GoToMyPC folks. As long as the remote drives are mounted in some standard way (usually as a shared network drive in these scenarios), Opus (and all other software) will be able to work with them. Opus can also work with standard FTP and SFTP connections, if they can provide access to the drives via that method.
From a quick look at the GoToMyPC website it looks like it uses a dedicated application (the "Viewer") to access remote files. If you can access your files through Explorer then it might be possible but if you have to use their application then I would guess not.