If you look through the manual, you will see the file types.
Also from the manual on page 2:
Sometimes books are protected using Digital Rights Management (DRM). DRM prevents unauthorized copying of books, and is often used to protect the books you get from libraries and booksellers. Your eReader can read EPUBs protected by Kobo DRM and non-protected EPUBs.
Now, the iOS App (for Apple devices) does handle ADE files. So it is not impossible that the Vox will too. Only Kobo staff know what the expected changes look like, over time. In the meantime, you can use Overdrive, Aldiko, and other programs for library books.
Those of us who have used Kobo devices for awhile know that Kobo very often introduces features first for their format and (very often fairly quickly) expands the functionality of different formats.