You'd set the UX1 as your sound device in Reason (under Audio). Plug headphones or speakers into the UX1 as well as plug your guitar into it. On the audio track in reason that you're recording to, put a Line6 guitar amp as an insert and monitor through Reason. If you hear unprocessed guitar you're moniotring direct off the UX1. You probably don't want that.
The nice thing is, since you have a license for more models in the UX1, those should also show up in Reason's version of the amp.