For this to be a good soil amendment you would need to change the molecules to a form that plants can take in, this requires both bacteria and fungi.
The particular juniper that is traditionally used for the dietary supplement is the "red cedar" an aromatic juniper with a white sap wood and blood red heart wood, also used for "cedar chests and cedar closets".
The ash is more basic than the wood so the change in pH would be different than if you used wood chips or the leaves for a mulch.
To get it right you would need to monitor the pH for a few months to see just how much of a change the ash effect was.
While I don't see any problem with trying the cedar ash on a test area, I would not go blindly forth since there are other properties contained in ash than those reported.