Can an iOS device be backed up to Google Drive?
I wouldn't call Google Drive an iCloud competitor. Google Drive (like Dropbox) is your hard drive on the Internet. Meaning you can see, and manipulate your files.

iCloud is a bit different, for starter, it's an Apple-centric service, you can backup your iOS devices, store your music (but only access it with iTunes), store your (iCloud) mail, calendar, reminders and contacts, and let apps store settings on it.  

But you can't access it directly like you would do with Dropbox or Google Drive.



So I would say that you will not be able to use Google Drive to back up your iOS devices as easily as you would do with iCloud.