You might want to read this short thread near the bottom:
If it is still true (I have not tried to Rewire Reason 8 yet), it makes using Reason+Rewire+Cubase amazingly cumbersome.
This is still the way it's working. Cumbersome - yes, but it's possible to make project templates in both Cubase and Reason that will help you avoid setting the whole thing up from scratch every time. I just made myself templates which includes 5 Reason instruments routed through rewire ch. to 5 group ch. in Cubase. By customizing the Cubase mixer I hide all rewire ch. and the group ch. appears next to the "normal" instrument ch. All I have to think of is opening Cubase and Reason in the right order and it will work just like that.