Does UV help at all in reducing counts?
Yes, however, whether it makes any practical difference to your fish is less clear. I run one, but it will not eradicate ich from your tank. You will have to remove all surviving fish and treat them as suggested while leaving your tank fish less for at least 72 days. Even a fish that does not die will likely be carrying the bug so any subsequent additions, even if run through QT, will be vulnerable.
IMO never add an ich-magnet like a Hippo without proper QT.