Can Reason be used as a plugin in a different host?
So what I would like to do, is bring Reason in as a VSTi into my host prog - is that possible, or do I have to have the full software running at same time as my host?
If your host program supports ReWire technology, you can use Reason from within your host program.
I have ReWired Reason into Adobe Audition, and it works for many other host programs. It's a little bit clumsy, but do-able.
For a Reason user, Propellerhead's Record offers absolute seamless integration with Reason, as well as audio recording capabilities. That has saved me time and made my workflow more effective. I don't consider Record to be a replacement for Audition 3, however.
If you don't have Reason yet, and are interested in Record, the most inexpensive way to get them would be to start by buying someones license for Reason 3. Then you could get Record for Reason owners for $149 USD and that would include a free upgrade to Reason 4.
For the money, I don't know of anything that comes close.