From the samples provided on the Vuforia website, it is supposedly "Possible" to get Video playback to work via Cloud Recognition targets; in particular storing the URL's in the JSON files and retrieving them within the app itself.
The demo's the provide explain the basic cloud reco and video playback (Offline videos or manually assigning a URL per video prefab), but no example of working together.
From using these samples from their website: [url removed, login to view] - specifically the "Advanced Topics" for the Video Playback and "Best Practices" for the Books Sample (Cloud Reco using JSON). Can you get video playback to worth via cloud reco with one singular cloud target and replacing the contents (The Books demo explains how to do Image and text replacement).
This may already be accessible via Google or if you manage to sift through the mess on their forums, or might be incredibly easy considering the vast majority of code is there; it looks like it (Hopefully) just needs some mixing of the two sample packs.