You can halo anything. I personally love the look with colored gemstones--its a nice contrast. I also think it is nice to halo cuts like ovals (in diamonds) that don't have a lot of sparkle, because the halo sparkles. I don't like RBs in haloes so much as it looks to me as if the person is trying to make their stone look bigger and I dislike step cuts with halos around them--doesn't seem to 'match' to me.
But to each their own.
But to each their own.