Any 3rd party module can take advantage of DNNGlobalStorage simply by using the DNN File System API (DNN Virtual File System) for all the file and folder related operation. The DNN core is using it everywhere, and many 3rd party vendors too.
By DNN File System API, module developers are abstracted from any knowledge about any cloud storage (S3, Box, etc.), FTP, UNC, or whatever. Example code to get a file's Url (no matter where it really is, if authentication is required or not, etc.:
var file = FileManager.Instance.GetFile(fileId);
Example code to get a file's content (as a stream). This code is valid for any local (standard) file, or files using the built-in "Secure" or "Database" providers, or files using GlobalStorage's "Box, "Google Drive" or whatever provider:
var file = FileManager.Instance.GetFile(fileId, true);
var content = FileManager.Instance.GetFileContent(file);
Example code to get the files in a given folder (again, it doesn't matter if the folder and files are actually local or in Amazon S3, Azure, an FTP server or whatever):
var folder = FolderManager.Instance.GetFolder(portalID, folderPath);
var files = FolderManager.Instance.GetFiles(folder, false, false);
You can find lots of examples about using properly the DNN File System API reviewing the DNN Core code (available in GitHub). Or perhaps, the built-in Intellisense in Visual Studio is enough.