Halos are more of a video post process as far as I can tell. This means they are rendered after the rest of the scene. This is why they can not appear in refelctions or cast shadows.
The easiest way to do what you want to do is to use buffered shadows. This means you can only use spotlight for shadow casting. The reason for this is that the spotlight is the only lamp that still supports buffered shadows. Buffered shadows are the shadows that are linked to those shadow buttons in the materials section. These shadows work the way you would think they should, not like raytraced shadows. The buffered shadows you can turn on and off with the buttons.
So build you scene around these limitations and you can achieve success. Otherwise, you have to go into nodes and separate passes and re-composite. A bunch of extra work, if you ask me. And there are bugs in that node system wich prevents colored shadows from separating correctly.
I am attaching an example BLEND that shows buffered shadows at work.
The blue sphere is a HALO texture.
The red sphere is reflecting, but no shadow.
The red cube is reflecting with shadow.
Attachments
ras_shadow_mirror.blend (375 KB)
