I have Webcam camera part of the vuforia plug-in (the only thing I wish to use it for) working on Unity 4.6 without any issues, just import the package and In an empty scene replace the camera with the AR camera prefab and build to andriod.. everything works fine, you can see the camera being displayed on the phone (Samsung Galaxy S3).
When I upgrade the project to the lastest Unity 5.1.2f (32 bit), and build the same project, All I get is a black screen.
I've made sure that the player settings for Andriod are identical to what they are in Unity 4.6. I have tried re-importing the Vuforia package.
The next step I was going to take was downloading an eariler version of Unity 5 and trying that.
If you have Vuforia working on Unity 5, could you share what specific version of Unity 5 you are using?
Any help would be greatly appreciated as I would prefer to use Unity 5.