I hated hotspot when it came in. Because it only ever really showed anything when there was a massive edge etc. But I have seen it develop over the past two years, and while it still won't show anything up off a feather of an edge, it is useful in determining stuff like whether the ball hit bat or pad first etc.
I think that would be a piece of technology that would be acceptable and quite useful for the 3rd ump, but as far as I know they can't use any of them. Although I can't be sure on Hotspot, I am basically 100% on the other two.