I have heard of cases (some members of TFF and others) where this seemingly works. For how long I'm not sure, but this combination is not advised. If the Angels are small and the shrimp large, it might work until the Angels are large enough to relentlessly hound down the shrimp. Again, in a very large well planted tank it might seemingly work for a while - but not fair on the shrimp to constantly live in fear of it's predator.